Physics Concepts - Chapters 7-9

Atmospheric pressure is caused by 1. the weight of air above a particular location. 2. clouds. 3. air currents. 4. the altitude above sea level.

1

You're driving in a convertible car with the top up and the windows closed. You note that the fabric top puffs up. To what can this phenomenon be attributed? 1. Bernoulli's principle 2. Both 3. Newton's Laws

1 Explanation: According to the principle of continuity, a fluid gains speed when it flows into a con- stricted region. Your car (convertible or oth- erwise) somewhat constricts the flow of mov- ing air, so by applying Bernoulli's principle, air moving over the top speeds up and pres- sure decreases. Reduced atmospheric pres- sure on the top of the fabric with no reduction in air pressure beneath (inside the car) pro- duces a pressure difference on the fabric and it puffs upward.

The pressure at the bottom of a 3-foot-deep lake miles in diameter is P1. The pressure at the bottom of a 3-foot-deep hot tub 2 meters in diameter is P2. What relationship would P1 and P2 have? 1. P1 = P2 2. Unable to determine 3. P1 < P2 4.P1 >P2

1 Explanation: Pressure only depends on the depth below the surface of the fluid, not on the amount of liquid, or on container shape or size.

What explains why a baseball pitcher could throw a curve ball? 1. Bernoulli effect 2. The ideal gas law 3. Archimedes' principles 4. Newton's third law

1 Explanation: The pitcher spins the ball. The air flow over one side of the ball is effectively greater than the air flow over the other side, which creates a pressure difference and a force in the direction of the low pressure side. This is known as Bernoulli effect.

If a viscous fluid flows steadily in a pipe, the fluid speed 1. is the same at the pipe wall and center but is smaller in between. 2. is least near the pipe wall but increases toward the center. 3. must be uniform across any cross section. 4. is the same at the pipe wall and center but is greater in between. 5. is greatest near the pipe wall but decreases toward the center.

2 Explanation: Since the fluid is viscous, the speed is in fact not uniform; the part near the pipe wall has the slower speed due to friction from the wall.

You want a blood pressure reading as close as possible to that of your heart. Where should you place the cuff? 1. at a level below the heart 2. at a level even with the heart 3. anywhere the cuff will fit 4. at a level above the heart

2 Explanation: By measuring the blood pressure at the same height (altitude) as the heart, the read- ing will be the same as that of your heart.

A plane usually extends flaps from its wings during takeoff and landing. What is a reasonable explanation? 1. The appearance of the plane would be great. 2. From the Bernoulli effect, this will create a larger upward force. 3. From Archimedes' principle, this will create more buoyant force. 4. This is a safety precaution and has nothing to do with the lift on takeoff.

2 Explanation: Extra area creates more upward force at a given speed. Once the plane is in flight and moving very fast, the extra area is not necessary.

Why does the pressure of a gas double (provided the temperature and volume of the container remain the same) if the number of gas atoms in container is doubled? 1. The attraction among the molecules doubles when the number of molecules doubles. 2. The frequency of the molecular collisions doubles when the number of molecules doubles. 3. The speed of the molecules doubles when the number of molecules doubles.

2 Explanation: Pressure is the force per unit area on the wall of the container. The force is due to the collisions of the gas molecules with the container walls. When the number of the molecules in the container is increased, the frequency of the molecular collisions with the wall increases proportionally.

Do the stones hurt your feet less or more in the water than on the stony beach? Explain. 1. As you enter the water they hurt more at first and then less; until we start floating we "sink" onto the stones, but once we start floating the displaced water lifts us up. 2. The stones hurt less in the water; the buoyant force lifts us up. 3. It feels exactly the same; our mass doesn't change, so we press down on our feet in the same way. 4. The stones hurt more in the water; the buoyant force increases as we go deeper.

2 Explanation: Your weight in water (what your feet feel) is the difference in your normal weight and the buoyant force (which increases as you go deeper in the water).

The brake system on a car is an example of 1. an inclined plane. 2. a lever. 3. a hydraulic device. 4. a simple machine.

3

What is not a fluid? 1. air 2. oil 3. sugar 4. water

3 Suger is a solid.

At what level (vertically) should you hold a cut finger to reduce bleeding? 1. as far from your heart as possible at any level 2. as low as possible 3. at the same level as your heart 4. as high as possible

4 Explanation: Liquid pressure depends on the height.

A helium filled balloon is floating, held down by a string, inside an accelerating car. If the car accelerates forward, which way does the balloon lean? 1. to the right 2. to the left 3. remains vertical 4. toward front of car 5. toward back of car

4 Explanation: Since the car is a noninertial (accelerated) frame with respect to the ground, when the car accelerates forward, the air is pushed back and the balloon is pushed forward by the air. because there is more pressure in the back of the balloon it pushes the helium, which is less dense, forward to the less dense part of the car

A ball rolls around a circular wall as shown. The wall ends at point X. When the ball reaches point X, which path will it follow? 1. Path D 2. Path E 3. Path A (circular path) 4. Path C (perpendicular - straight line path) 5. Path B (kind of circular)

4. As soon as the ball reaches point X the centripetal force is removed, so the ball moves in a straight line (tangent to the circle at point X).

Can the battleship USS Iowa float in a bath- tub? Of course, you have to imagine a very big bathtub or a very small battleship. In either case, there is just a bit of water all around and under the ship so this battle- ship does float. Specifically, suppose the ship weighs 100 tons (a "pocket battleship" you may call) and the water in the tub weighs 100 pounds. Determine the buoyant force B. 1. B = 100 pounds 2. 100 pounds < B < 100 tons 3. B < 100 pounds 4. B > 100 tons 5. B = 100 tons.

5 Since the "pocket battleship" is floating, there are only two forces acting on it, the weight and the buoyant force. Furthermore, it is stationary, the net force on it must be zero too. mg - B = 0 B = mg = 100 tons

What is the kinetic energy of a satellite of mass m that orbits the Earth of mass M in a circular orbit of radius R? 1. K = 0 2. K = 1/2 GMm/R^2 3. K = G M m/R^2 4. K = 1/4 G M m/R 5.K = 1/2 GMm/R

5 The gravitational force on the satellite pro- vides the centripetal force needed to keep it in circular orbit: GMm/R^2 = Fg = Fc = m(v^2/R) (centripetal force is a net force and the only force acting on the satellite. you have to set it equal to the force of gravity) mv^2 = GMm/R so, K = 1/2 mv^2 = 1/2 GMm/R

If a liquid only half as dense as mercury were used in a barometer, how high would its level be on a day of normal atmospheric pressure (when the mercury barometer reads 76 cm)? 1. 76 cm 2. 38 cm 3. 304 cm 4. 19 cm 5. 152 cm

5 density = Mass/Volume Mass = Density X volume Thus for a given mass, halving the density means the volume must be doubled. For a tube with a given radius, twice the volume means twice the height.

A floating ball normally weighs 6.7 N. The acceleration of gravity is 9.8 m/s2 . What is the size of the buoyant force that acts on it?

6.7 N The buoyant force is equal to the weight lost by the object and a floating object is weightless in the fluid

A cat usually lands on its feet regardless of the position from which it is dropped. A slow-motion film of a cat falling shows that the upper half of its body twists in one direction while the lower half twists in the opposite direction. Why does this type of rotation occur?

As the cat falls, angular momentum must be conserved. Thus, if the upper half of the body twists in one direction, something must get an equal angular momentum in the opposite direction. Rotating the lower half of the body in the opposite direction satisfies the law of conservation of angular momentum

The water supply for a city is often provided from reservoirs built on high ground. Water flows from the reservoir, through pipes, and into your home when you turn the tap on your faucet. Why is the water flow more rapid out of a faucet on the first floor of a building than in an apartment on a higher floor?

At lower elevation, the water pressure is greater because pressure increases with increasing depth below the water surface in the reservoir (or water tower). The penthouse apartment is not so far below the water's surface. The pressure behind a closed faucet is weaker there and the flow weaker from an open faucet. Your fire department likely has a record of the precise elevation of every fire hydrant. The flow of water depends upon the difference in pressure between the pressure in the pipe and the air pressure outside the pipe. The air pressure is essentially the same on the first floor or a higher floor because the density of air is small (compared to the density of water). However, the water pressure will decrease as the altitude increases. This means the difference in pressure between water pressure inside the pipe and air pressure outside the pipe will be smaller as one's altitude increases.

Four solid, uniform objects are placed in a container of water. Rank their densities from highest to lowest.

D, A, C, B

Moment of inertia for a long, thin rod with rotational axis through its center

I = 1/12ML^2

Moment of Inertia for a solid cylinder or disk

I = 1/2MR^2

Moment of Inertia for a long, thing rod with rotation axis through the end

I = 1/3 ML^2 a door turning on is hinges is described by this same moment of inertia

Moment of Inertia for a thin spherical shell

I = 2/3 MR^2

Moment of Inertia for a solid sphere

I = 2/5MR^2

Moment of Inertia for a hoop

I = MR^2

Will an ice cube float higher in water or in an alcoholic beverage?

Ice cubes will float lower in a mixed drink because the mixture of alcohol and water is less dense than water. In a less dense liquid a greater volume of liquid must be displaced to equal the weight of the floating ice. Density of water is approx 1g/ml Density of Ice is approx 0.93g/ml Denisty of 100% pure ethanol is 0.79g/ml Thus Ice would not float at all in 100% pure ethanol. alcohol is less dense than ice so ice will sink

Why can't you put your heels firmly against a wall and then bend over without falling?

In order for you to remain in equilibrium, your center of gravity must always be over your point of support, *the feet*. If your heels are against the wall, your center of gravity cannot remain above your feet when you bend forward, so you lose your balance. center of mass cannot change if you are against a wall.

Is it possible for a car to move in a circular path in such a way that it has a tangential acceleration but no centripetal acceleration?

NO. Any object that moves such that the direction of its velocity changes had an acceleration. A car moving in a circular path will always have a centripetal acceleration.

If you see an object rotating, is there necessarily a net torque acting on it?

No. An object in motion will remain in motion until an applied force changes it. A net torque is not required to keep the object rotating if it is already rotating.

For a figure skater, how will pulling arms and legs in affect moment of inertia and angular speed?

Pulling in his arms and legs will reduce his moment of inertia this increasing his angular speed. the opposite is true upon landing - extending his arms and legs will increase his moment of inertia thus decreasing his angular speed (rate of spin)

The density of air is 1.3 kg/m^3 at sea level. From your knowledge of air pressure at ground level, estimate the height of the atmosphere. As a simplifying assumption, take the atmosphere to be of uniform density up to some height, after which the density rapidly falls to zero. (In reality, the density of the atmosphere decreases as we go up.)

Space officially begins at 100km, or 62.2 miles; but there's still some trace atmosphere that a satellite would need to contend with. To answer the question as it was intended (not as nature "really works"), use the fact that air pressure at ground level is 101.3 kPa. The question then is, since pressure = rho g h, plug in rho and g and find h. 101,300 Pa = (1.3 kg/m^3) (9.8 m/s^2) h Noting that 1 Pa = 1 N/m^2 = 1 kg/(m s^2), we will get h in meters, it's 7951 meters = about 8 km. This is sometimes called the "equivalent height" of the atmosphere, meaning exactly that it's the height the atmosphere would have if you could somehow force all of it to have the same density it has at the bottom. 100,000/(1.3 x 9.8) = 7849 m or 7.8 km about 8 km

Why does a long pole help a tightrope walker stay balanced?

The long pole had a large moment of inertia about an axis along the rope. An unbalanced torque will then produce only a small angular acceleration of the performer-pole system, to extend the time available to regain balance The pole helps to stabilize their center of mass. If the person begins to lean to the left, the right side of the pole can be tilted downward to correct the shift of weight and will become stable again. A long pole increases the moment of inertia of the tightrope walker(recall moment of inertia varies as mr2; hence long poleequals larger r). We know that angular momentum is L = Iω. If the tightrope walker starts losing his balance on the rope, he will rotate around the rope a lot more slowly with a large moment of inertia than if he had a small moment of inertia. This buys him time, so to speak, to adjust the pole and re-balance himself.

An object executes circular motion with constant speed whenever a net force of constant magnitude acts perpendicular to the velocity. What happens to the speed if the force is not perpendicular to the velocity?

The speed changes. Explanation: The tangential force component causes tangential acceleration. The component of force tangential to the path causes a tangential acceleration.

If a car's wheels are replaced with wheels of greater diameter, will the reading of the speedometer change? Explain:

The speedometer will be inaccurate. The speedometer measures the number of tire revolutions per second, so its reading will be too low bc you are going faster. you are going 73 instead of 70. It will be lower because if the radius goes up, the angular velocity will increase since they are indirectly proportionate. (Velocity tangential = Radius x angular velocity)

An ice cube is placed in a glass of water. What happens to the level of the water as the ice melts?

The water level remains the same when the ice cube melts. A floating object displaces an amount of water equal to its own weight. Since water expands when it freezes, one ounce of frozen water has a larger volume than one ounce of liquid water

7.5 When the merry-go-round of 7.4 is rotating at a constant angular speed, Andrea's tangential speed is a) twice Chuck's b) the same as Chuck's c) half of Chuck's d) impossible to determine

a

Which of the following will sink in water? (Density = 1g/cm^3 a. Balsa wood (0.12 g/cm^3) b. steel (7.18 g/cm^3) c. cooking oil (0.82 g/cm^3) d. ethyl alcohol (0.798 g/cm^3)

b Objects with larger densities will sink

9.5 Atmospheric pressure varies from day to day. The level of a floating ship on a high-pressure day is a) higher b) lower c) no different than on a low-pressure day

c pushing on the water more but also pushing on the boat more and because of that it just stays the same it is getting the same amount of net change

7.10 Suppose an asteroid has a semi-major axis of 4 AU. How long does it take the asteroid to go around the sun? a) 2 years b) 4 years c) 6 years d) 8 years

d

A solid disk and a hoop are simultaneously released from rest at the top of an incline and roll down without slipping. Which object reaches the bottom first? a) the one that has the largest mass arrives first. b) the one that has the largest radius arrives first c) the hoop arrives first d) the solid disk arrives first e) the hoop and the disk arrive at the same time

d Explanation: The disk gets there first because it has the smaller moment of inertia, so less of the energy finishes up as rotational energy, instead becoming translational energy and getting the disc moving faster. a hoop and a disc have different moments of inertia. the bigger the I the more it resists rotation hoop I = mr^2 whereas solid disc is I = 1/2mr^2 since it has a smaller moment of inertia is resists rotation less so it will move faster.

8.1 Using a screwdriver, you try to remove a screw from a piece of furniture, but can't get it to turn. To increase the chances of success, you should use a screwdriver that is a. longer b. shorter c. has a narrower handle d. has a wider handle

d a wider handle has a bigger radius. a longer handle would be for a wrentch

A block of aluminum with a volume of 9 cm is placed in a beaker of water filled to the brim and sinks. Water overflows. The same happens in another beaker with a 9 cm3 block of lead. The lead will displace (more, less, the same amount of) water than the aluminum block does. 1. It cannot be determined without a direct measurement. 2. more 3. less 4. the same

d = m/v The two blocks have the same volume, so they will displace the same volume of water.

A mouse is initially at rest on a horizontal turntable mounted on a frictionless, vertical axle. As the mouse begins to walk clockwise around the perimeter, which of the following statements must be true of the turntable? a) It also turns clockwise b) It turns counterclockwise with the same angular velocity as the mouse c) it remains stationary d) It turns counterclockwise because angular momentum is conserved e) It turns clockwise because mechanical energy is conserved

d) It turns counterclockwise because angular momentum is conserved

7.9 A planet has two moons with identical mass. Moon 1 is in a circular orbit of radius r. Moon 2 is in a circular orbit of radius 2r. The magnitude of the gravitational force exerted by the planet on Moon 2 is a) four times as large b) twice as large c) the same d) half as large e) one fourth as large as the gravitational force exerted by the planet on Moon 1

e

The three containers are filled with water to the same level. Rank the pressures at the bottom of the containers a) Pa>Pb>Pc b) Pa>Pb=Pc c) Pa=Pb>Pc d) Pa<Pb<Pc e) Pa=Pb=Pc

e Pressure at the bottom of container will be given by: P = rho*g*h since height for all of the containers are same, So pressure at the bottom will be same for all three containers, P1 = P2 = P3

The cars in a soapbox derby have no engines; they simply coast downhill. Which of the following design criteria is best from a competitive point of view? The car's wheels should (a) have large moments of inertia (b)be massive (c) be hoop-like wheels rather than solid disks (d) be large wheels rather than small wheels (e) have small moments of inertia

e) The car's wheels should have small moments of inertia Explanation: Moment of Inertia is the force needed to get things moving, so a smaller MoI would get the derby cart going faster. smaller moment of inertia because it will then resist rotation less so it will move faster.

During inhalation, the pressure in the lungs is slightly less than external pressure and the muscles controlling exhalation are relaxed. Under water, the body equalizes internal and external pressures. Discuss the condition of the muscles if a person under water is breathing through a snorkel. Would a snorkel work in deep water?

no The external pressure exerted on the chest by the water makes it difficult to expand the chest cavity and take a breath while under water so it would not be possible to use a snorkel in deep water. No. To be able to breathe in deep water you would need to exert pressure to on the water to be able to expand your lungs to suck in air. Without the high pressure air that would help to balance the water pressure, it would be difficult to expand your lungs.

Figure shows aerial views from directly above two dams. Both dams are equally long (the vertical dimension in the diagram) and equally deep (into the page in the diagram). The dam on the left holds back a very large lake, while the dam on the right holds back a very narrow river. Which dam has to be built more strongly?

they would be the same, regardless of how much water is behind the dam. Both dams must be equally strong. Since the force on the back of each dam is the average pressure x the area. Here, both dams are equally deep thus average pressure is the same, and force is the same.

Harry and Sue cycle at the same speed. The tires on Harry's bike have a larger diameter than those on Sue's bike. Which tires have the greater rotational speed? 1. The rotational speeds are the same. 2. It depends on the speed. 3. Sue's tires 4. Harry's tires

3. Sue's tires Why? v = r ω. Tires with a smaller radius needs a larger rotational speed to obtain the same linear speed. w = v/r if r goes down w goes up.

A person stands a distance R from a door's hinges and pushes with a force F directed perpendicular to its surface. By what factor does the applied torque change if the person's position and force change to (a) 2R and 2F (b) 2R and F, (c) R and F/2, (d) R/2 and F/2

T = R x F a. 4RF b. 2RF c. RF/2 d. RF/4

9.6 The density of lead is greater than iron, and both metals are denser than water. Is the buoyant force on a solid lead object a) greater than b) equal to c) less than the buoyant force on a solid lead object of the same dimensions?

They will be the exact same since the volume is the same and the gravity is the same. Rho is referring to the Rho of the fluid underneath the object. They are the exact same so the buoyant force is the exact same.

9.7 You observe two helium balloons floating next to each other at the ends of strings secured to a table. The facing surfaces of the balloons are separated by 1-2 cm. You blow through the opening between the balloons. What happens to the balloons? a) They move toward each other b) They move away from each other c) They are unaffected

a they will move toward each other you decrease the pressure since you increase the speed. if you decrease the pressure in between them the pressure on the outside is pushing them toward each other. increasing velocity term and decreasing the pressure term P1 + 1/2 rho v^2 = P2 + 1/2 rho v^2

A disc rotates about an axis through its center. Point A is located on its rim and point B is located exactly halfway between the center and the rim. What is the ratio of (a) the angular velocity wa to that of wb and (b) the tangential velocity va to that of vb?

a) 1.00 Both of them are moving with an equal angle although they are a different distance from the center. Because of this, there is a ratio of 1. b) 2.00 The tangential speed is the linear speed it would be going if it didn't have centripetal acceleration. A is moving more distance over the same amount of time as B. It is moving double the distance since the radius of B is half of the radius of A. V = rw A = 2w B = 1w

Two point masses are the same distance R from an axis of rotation and have moments of inertia Ia and Ib. (a) If Ib = 4Ia, what is the ratio mb/ma of the two masses? (b) At what distance from the axis of rotation should mass A be placed so that Ib = Ia?

a) Ib/Ia = 4 so mb/ma =4 b) 2R x^2 = mbR^2/ma = x = square root of mbR/ma = 2R

Orbiting spacecraft contain internal gyroscopes that are used to control their orientation. (a) Apply the principle of conservation of angular momentum to determine the direction a spacecraft will rotate if an internal gyroscope begins to rotate in the counterclockwise direction. (b) How many mutually perpendicular gyroscopes with fixed axes of rotation are required to have full control over the spacecraft's orientation?

a) clockwise - to cancel it out. angular momentum has to be conserved. b) 3 because there are 3 dimensions. x, y, and z

Equal volumes of two fluids are added to the U-shaped pipe as shown in Figure. The pipe is open at both ends and the fluids come to equilibrium without mixing. (a) Which fluid has the higher density, fluid A or fluid B? (b) What is the ratio Pb/Pa of the fluid densities?

a) fluid B Pressure = Rho x g h since the pressure is the same at the top of both, the height for fluid A is higher which means its rho is smaller. Thus fluid B has a greater rho thus it is more dense. b) 4 ghA/ghB = Pb/Pa hA/hB = Pb/Pa the h of B is 1 and the h of A is 4 so it is Ha/Hb = 4/1

A car of mass m follows a truck of mass 2m around a circular turn. Both vehicles moved at speed v. (a) What is the ratio of the truck's net centripetal force to the car's net centripetal force? (b) At what new speed vtruck will the net centripetal force acting on the truck equal the net centripetal force acting on the car still moving at the original speed v?

a) mv^2/r everything is the same except for the masses, so 2:1 ratio b) the square root of v/2

Water flows along a streamline through the pipe shown in figure. Point A is higher than points B and C, and the pipe has a constant radius until it expands between B and C. From highest to lowest, (a) rank the flow speeds at points A, B, and C and (b) rank the pressures at points A, B, and C.

a) va=vb>vc b) Pc>Pb>Pa P = F/A (A) flow rate = A v so smaller the area and greater will be speed. vA = vB > vC (B) P + rho g h + rho v^2 /2 = constant h decreases so P increases. Pa < Pb now v decrease so Pc > Pb Pc > Pb > Pa

7.1 A rigid body is rotating counterclockwise about a fixed axis. Each of the following pairs of quantities represents an initial angular position and a final angular position of the rigid body. Which of the sets can occur only if the rigid body rotates through more than 180 degrees? a) 3 rad, 6 rad b) -1 rad, 1 rad c) 1 rad, 5 rad

c

A child is practicing for a BMX race. His speed remains constant as he goes counterclockwise around a level track with two nearly straight sections and two nearly semicircular sections, as shown in the aerial view of the figure. (a) What are the directions of his velocity at points A, B, and C? For each point, choose one: north, south, east, west, or nonexistent. (b) What are the directions of his acceleration at points A, B, and C?

(a) A-north B-west C- south (b) A-west B- nonexistent C- east Explanation: A < C= D >B = E Points B and E show zero acceleration bc speed is constant Points C and D have equal acceleration

(a) Give an example in which the net force acting on an object is zero, yet the net torque is nonzero. (b) Give an example in which the net torque is zero, yet the net force is nonzero.

(a) Consider two people pushing with equal magnitude forces in opposite directions and at opposite ends of a table. The net force will be zero, yet the net torque is not zero. radius is from the center of mass to where the force starts from center of mass to where the force begins is radius*** because of this the radius is pointing down towards the leg and so the force being exerted on the table is perpendicular to the radius. Thus there is torque If you have a disc and both forces are going clockwise then you have a net force of zero but you have a net torque of nonzero. (b)Consider a falling body. The net force acting on it is its weight, yet the net torque about the center of gravity is zero. when you have a disc and one force is pulling counterclockwise while the other is pulling clockwise, this would result in a net torque of zero and a net force of nonzero.

Describe the path of a moving object in the event that the object's acceleration is constant in magnitude at all times and (a) perpendicular to its velocity; (b) parallel to its velocity.

(a) If the acceleration is constant in magnitude and perpendicular to the velocity, the object is moving in a circular path at constant speed. (b) If the acceleration is parallel to the velocity, the object moves in a straight line, and is either speeding up (v and a in same direction) or slowing down (v and a in opposite direction)

A pendulum consists of a small object called a bob hanging from a light cord of fixed length, with the top end of the cord fixed, as represented. The bob moves without friction, swinging equally high on both sides. It moves from its turning point A through point B and reaches its maximum speed at point C. (a) At what point does the bob have non-zero radial acceleration and zero tangential acceleration? What is the direction of its total acceleration at this point? (b) At what point does the bob have nonzero tangential acceleration and zero radial (centripetal) acceleration? What is the direction of its total acceleration at this point? (c) At what point does the bob have both nonzero tangential and radial acceleration? What is the direction of its total acceleration at this point?

(a) Point C. The total acceleration here is centripetal acceleration, straight up. (this is pointing to the center of the circular motion) tangential acceleration at this point is zero because the the tension and mg are equal to eachother. nothing in the x direction that causes tangential acceleration. (b) Point A. The speed at A is zero where the bob is reversing direction. The total acceleration here is tangential acceleration, to the right and downward perpendicular to the cord. we are unbalanced in the x direction, therefore there is tangential acceleration in the x direction Because there is no velocity at the change in direction there is also no acceleration. (c) Point B. The total acceleration here is to the right and pointing in a direction somewhere in between the tangential and radial directions, depending on their relative magnitudes

Which planets have a period of rotation around the Sun greater than 1 Earth year? 1. Those farther from the sun 2. Additional information is needed. 3. Those closer to the sun 4. It depends on the planet's mass.

1 From Kepler's third law, the period is greater when the distance is greater, so the periods of planets farther from the sun are longer than our year.

Why do ice cubes float? 1. Ice cubes are less dense than water. 2. Ice cubes are lighter than water. 3. Ice cubes are in a solid state.

1 Ice cubes are less dense than water. If ice were more dense than water, it would sink, and the bottom of ponds and oceans could be covered by ice during the winter.

When you pedal a bicycle with a constant downward force, is maximum torque produced when the pedal sprocket arms are in the horizontal position, in the vertical position, or in the diagonal position? 1. horizontal position 2. vertical position 3. All torques are the same. 4. diagonal position

1 The maximum lever arm is when the pedal sprocket arm is horizontal (lever = radius), with the minimum at the vertical orientation (lever arm = 0).

7.6 A racetrack is constructed such that two arcs of radius 80 m at A and 40 m at B are joined by two stretches of straight track as in figure. In a particular trial run, a driver travels at a constant speed of 50 m/s for one complete lab 1. The ratio of the tangential acceleration at A to that at B is a) 1/2 b) 1/4 c) 2 d) 4 e) The tangential acceleration is zero at both points. 2. The ratio of the centripetal acceleration at A to that at B is a) 1/2 b) 1/4 c) 2 d) 4 e) The centripetal acceleration is zero at both points 3. The angular speed is greatest at a) A b) B c) It is equal at both A and B

1. e 2. a 3. b ??? angular speed is greater at a smaller radius than a larger radius**`

What do we call the gravitational force be- tween the earth and your body? 1. mass 2. velocity 3. Newton 4. gravitation 5. weight

5 Weight is defined as the force due to gravity on a body.

It has been suggested that rotating cylinders about 10 miles long and 5 miles in diameter be placed in space for colonies. The purpose of their rotation is to simulate gravity for the inhabitants. Explain the concept behind this proposal.

Consider an individual standing against the inside wall of the cylinder with her head pointed toward the axis of the cylinder. As the cylinder rotates, the person tends to move in a straight-line path tangent to the circular path followed by the cylinder wall. As a result, the person presses against the wall, and the normal force exerted on her provides the radial(centripetal) force required to keep her moving in a circular path. If the rotational speed is adjusted such that this normal force is equal in magnitude to her weight on Earth, she will not be able to distinguish between the artificial gravity of the colony and ordinary gravity.

Suppose an alien civilization has a space station in circular orbit around its home planets. The station's orbital radius is twice the planet's radius. (a) If an alien astronaut has weight w just before launch from the surface, will she be weightless when she reaches the station and floats inside of it? (b) If not, what will be the ratio of her weight in orbit to her weight on the planet's surface?

F = G(M1m2) / r^2 a) No, she will not be weightless. There is still a little bit of gravity acting on her from the planet b) Her weight in orbit will be one fourth less than her weight on the planet's surface. This is because the radius is twice as big and as you double the radius, since it is squared, it will quadruple. And when radius increases, force (being indirectly proportionate) will decrease by a factor of four.

(a) Is it possible to calculate the torque acting on a rigid object without specifying an origin? (b) Is the torque independent of the location of the origin?

NO! It is easy to state "find the torque caused by these forces". But that is a meaningless statement. What is always required -- or meant or implied -- is "find the torque with respect to such-and-such center of rotation that is caused by these forces". Sometimes -- because of a drawing or some limitation such as the hinges on a door -- we may not specifically state that "with respect to such-and-such center of rotation" but that information is required before the statement has any meaning! if you think about it a torque vector is oriented in the 3D-Euclidian space. the point of orientation is relative to some orgin in a chosen coordinate system. Now if you take the coordinate system away then you just have the vector part of the torque. this would imply that the direction and magnitude of the torque would be assumed and not computed, because the torque equation doesn't allow it to calculated without the origin specified(i.e. transformations from manifold-to-maniflold can occur). therefore, the torque cannot be computed without an origin, because it would cease to exist as a torque vector.this might not seem so obvious, but try the following problem and take away the origin from your coordinate system and try the same problem with the origin in the coordinate system(hint: use spherical coordinates). think about the torgue developed by the rotation of the Earth go through the calculation. keeping what I previously said in mind one should realize the validity of this rationalization No, the axis must be specified: torque = (distance from the axis) X (force). (X is the vector cross-product in this case - meaning the angle also matters.)

Stars originate as large bodies of slowly rotating gas. Because of gravity, these clumps of gas slowly decrease in size. What happens to the angular speed of a star as it shrinks? Explain.

The angular momentum of the gas cloud is conserved. Thus the product Iω remains constant. Hence, as the cloud shrinks in size, its moment of inertia decreases, so its angular speed ω must increase L (angular momentum) = Iω moment of inertia = mr^2 So if the size decreases the moment of inertia also decreases since it is related to the radius. (mr^2)(w) = (mr^2)(w) if the radius decreases the angular speed must increase since they are indirectly proportionate.

A pail of water can be whirled in a vertical circular path such that no water is spilled. Why does the water remain in the pail, even when the pail is upside down above your head?

The tendency of the water is to move in a straight-line path tangent to the circular path followed by the container. As a result, at the top of the circular path, the water presses against the bottom of the pail, and the normal force exerted by the pail on the water provides the radial force required to keep the water moving in its circular path. centripetal acceleration downward due to gravity. This means that the bucket is pushing down on the water and so the water is pushing against the pail the centripetal acceleration of the water is greater than the acceleration of the gravity meaning it will push against the bucket and not fall out.

Is it possible for a situation to exist in which the net torque acting on the object is zero while the net force acting on the object is not equal to zero. 1. Yes 2. No

Yes Explanation: Yes again — for example, just one force acting on the center of mass of an object produces no torque, but certainly produces a net force!

8.3 The two rigid objects show in figure have the same mass, radius, and angular speed, each spinning around an axis through the center of its circular shape. If the same braking torque is applied to each, which takes longer to stop? a) a solid disc b) a hoop c) more information needed

b solid disc I = 1/2MR^2 hoop I = MR^2 therefore, the moment of inertia is greater for a hoop requiring more time to stop it. the moment of inertia of a system depends on how the mass is distributed and on the location of the axis of rotation.

If you toss a textbook into the air, rotating it each time about one of the three axes perpendicular to it, you will find that it will not rotate about one of those axes. (Try placing a strong rubber band around the book before the toss so that it will stay closed.) The book's rotation is stable about those axes having the largest and smallest moments of inertia, but unstable about the axis of intermediate moment. Try this on your own to find the axis that has this intermediate moment of inertia.

the axis passing through the center of the textbook and perpendicular to its spine Explanation: The principle axis that runs along the shortest, intermediate, and longest edges each go through the books center of mass, and those axes have the highest, intermediate, and lowest moment of inertia respectively, so the intermediate moment of inertia would be the middle of the spine. the one axis where the length and width are constantly switching it will not rotate.

Once ski jumpers are airborne, why do they bend their bodies forward and keep their hands at their sides?

they try to reduce air friction and form an airfoil to produce lift They are trying their best at being an airplane wing so they can get the greatest distance. the difference in pressure between the underside and top of the wing creates a dynamic upward lift force this effect, the decrease the pressure on the top, the air is moving faster above the person so their is less pressure pushing him down. The air is moving slower underneath so there is more pressure. therefore, he is creating more lift. This is bernoullis affect.

A long string attached to a mass M forms a simple pendulum. The string, however, is weak enough so that it is likely to break at some point in the oscillation if you let it swing. You pull the mass back and start it oscillating. At what point in the cycle is the string most likely to break? 1. Just after release. 2. Just when the mass passes through the point where the string is vertical. 3. Just after the mass turns around to return. 4. Just after the mass returns to the starting point. 5. It is equally likely to break at all positions.

2 Since the string is weak, we must examine the tension in the string to determine at what point it will break. The tension T is given by T = Mgcosθ. When theta is zero, the tension is a maximum, so that the string will be most likely to break when it is vertical.

A long track balanced like a seesaw supports a mass m and another of mass 2m with a compressed spring between them. When the spring is released, the masses move away from each other. Does the track tip clockwise, tip counter- clockwise, or remain in balance as the masses move outward? Why? 1. tip counterclockwise; angular inertia 2. remain in balance; conservation of momentum 3. tip clockwise; center of gravity 4. remain in balance; angular frequency

2 Explanation: The track will remain in equilibrium as the masses move outward because the center of gravity (CG) of the system remains over the fulcrum. By conservation of momentum, the heavier mass will move outward at half the speed of the lighter one, and at any time be half as far from the starting point as the lighter one, so there is no CG change in the system of the two masses. We can see also that the torques produced by the weights of the masses multiplied by their relative distances from the fulcrum are equal at all points, be- cause at any time the less massive object has a correspondingly larger lever arm.

You sit at the middle of a large turntable at an amusement park as it is set spinning on nearly frictionless bearings, and then allowed to spin freely. When you crawl toward the edge of the turntable, does the rate of the rotation increase, decrease, or remain unchanged, and why? 1. decreases; conservation of energy 2. increases; conservation of momentum 3. decreases; conservation of momentum 4. increases; conservation of energy

3 Explanation: The rotational inertia of the system (you and the rotating turntable) is least when you are at the rotational axis. As you move outward, the rotational inertia of the system increases. Applying conservation of angular momentum, as you move toward the outer rim, you increase the rotational inertia of the spinning system, thus decreasing the angular speed. Also, if you don't slip as you move out, you exert a friction force on the turntable opposite to its direction of rotation, thereby also slowing it down.

9.2 The pressure at the bottom of a glass filled with water (rho = 1000 kg/m^3) is P. The water is poured out and the glass is filled with ethyl alcohol (rho = 806 kg/m^3). The pressure at the bottom of the glass is now a) smaller than P b) equal to P c) larger than P d) indeterminate

a because alcohol is less dense so Po + rho g h is less than that of water

An object is acted on by a single nonzero force of magnitude F. (a) Is it possible for the object to have zero acceleration a? (b) Is it possible for the object to have zero angular acceleration a? (c) Is it possible for the object to be in mechanical equilibrium?

a) no, not possible b) yes. You need a torque, force and radius must be perpendicular. So because there is only a singular force, there is not another perpendicular force or torque acting on it, therefore it doesn't have angular acceleration. c) NO. it is not possible for the object to be in mechanical equilibrium since there is a single force acting on it. If there was no force, no acceleration and no angular acceleration than it would be possible. The forces must cancel out to be in equilibrium

7.3 Consider again the pairs of angular positions for the rigid object in 7.1. If the object starts from rest at the initial angular position, moves counterclockwise with constant angular acceleration, and arrives at the final angular position with the same angular velocity in all three cases, for which choice is the angular acceleration the highest. a) 3 rad, 6 rad b) -1 rad, 1 rad c) 1 rad, 5 rad

b

7.2 . Suppose the change in angular position for each of the pairs of values in 7.1 occurred in 1 second. Which choice represents the lowest average angular velocity? a) 3 rad, 6 rad b) -1 rad, 1 rad c) 1 rad, 5 rad

b w = theda/seconds

9.1 Suppose you have one cubic meter of gold, two cubic meters of silver, and six cubic meters of aluminum. Rank them by mass, from smallest to largest. a) gold, aluminum, silver b) gold, silver, aluminum c) aluminum, gold, silver d) silver, aluminum, gold

c

8.5 A horizontal disk with moment of inertia I(1), rotates with angular speed w1 about a vertical frictionless axle. A second horizontal disk having moment of inertia I2 drops onto the first, initially not rotating but sharing the same axis as the first disk. Because their surfaces are rough, the two disks eventually reach the same angular speed w. The ratio of w/w1 is equal to a) I1/I2 b) I2/I1 c) I1/(I1+I2) d) I2/(I1+I2)

c Iw = (I 1 + I 2) W2 ; because they are sharing an axis for the second, you have to add their moments of inertia together. then divide and get I / I1 + I2

9.3 Several common barometers are built using a variety of fluids. For which fluid will the column of fluid in the barometer be the highest? a) mercury b) water c) ethyl alcohol d) benzene

c ethyl alcohol is the LEAST dense. a barometer measures the pressure of the atmosphere. because it is so much LESS dense, it is least affected by the atmospheric pressure, thus rising and being the highest. if Po is the same for all of them, the rho has to be smaller to make the height bigger Po = rho g h

Objects moving along a circular path have a centripetal acceleration provided by a net force directed towards the center. Identify the force(s) providing the centripetal acceleration in each of these cases: (a) a planet in circular orbit around its sun; (b) a car going around an unbanked, circular turn; (c) a rock tied to a string and swung in a vertical circle, as it passes through its highest point; and (d) a dry sock in a clothes dryer as it spins in a horizontal circle.

**the acceleration that causes angular motion** a) The suns gravity is pulling on the earth to keep it from going in a straight line. b) The frictional force exerted from the ground is pulling the car towards the center allowing it to have centripetal acceleration c) at the highest point, the only force acting on it is gravity which is providing a centripetal acceleration on the rock. d) the normal force from the walls of the dryer is what is keeping the sock moving which is causing a centripetal acceleration. The sock on the wall is exerting a force. the force is always pointed towards the center of the circular motion.

In a deep dive, a whale is appreciably compressed by the pressure of the surrounding water. What happens to the whale's density? 1. It cannot be determined. 2. Its density increases. 3. Its density remains the same as before. 4. Its density decreases.

2 Since the mass is unchanged and the volume decreases, the density of the whale increases D = m/v

A Ferris wheel rotates at a constant rate. A 150 lb student has an apparent weight of 125 lb at the top. What is her apparent weight at the lowest point? 1. 100 lb 2. 225 lb 3. 175 lb 4. 200 lb 5. 125 lb 6. 150 lb

3 Let: W=150lb and WT =125lb. The apparent weight is the force which the chair exerts on the rider. At top, the centripetal force required is downward, which is the difference between the downward weight and the upward force which the seat exerts on her, i.e. W−WT =mv2/R At the bottom, the centripetal force required is upward, which is the difference between the upward force exerted by the seat on her and her downward weight, i.e. WB − W = mv2/R WB = W + m v2/R = W + (W − WT ) = 2 W − WT = 2 (150 lb) − 125 lb = 175 lb

When you push on an object such as a wrench, a steel pry bar, or even the outer edge of a door, you produce a torque equal to the force applied times the lever arm. At what angle to the lever arm should a force be applied to produce maximum torque and why? 1. At any angle; the torque equals the force times the lever arm, and both of these remain the same. 2. At any angle; the torque is zero under all situations. 3. 90◦; this maximizes the effective length of the lever arm. 4. 0◦; this maximizes the effective length of the lever arm. 5. 180◦; this maximizes the effective force. 6. 90 degrees; the force would be parallel to the lever arm, so the torque is constant 7. 180 degrees; this maximizes the effective length of the lever arm 8. 0 degrees; this maximizes the effective force

3 Explanation: A 90◦ angle imparts the longest lever arm.

Which situation is likely to hurt you more? 1. Unable to determine 2. Your bare foot was stepped on by a 270-lb man wearing flat-soled loafer. 3. Your bare foot was stepped on by a 130-lb woman wearing high heels. 4. Either

3 P = F/A Pressure increases for a given force when the area decreases

A friend incorrectly says that a body cannot be rotating when the net torque acting on it is zero. What is the correct statement? 1. Once a body starts rotating the net torque is zero. 2. A body can have an angular velocity only when a non-zero net torque is acting on it. 3. A body's angular velocity cannot change if the net torque acting on it is zero and the moment of inertia does not change. 4. The original statement made by the friend is actually correct.

3 The rate and direction of rotation of a body cannot change when a zero net torque acts on it. Once started rotating, a body will continue rotating even when no torque acts on it. Again, emphasize change. (Net torque = Moment of Inertia x Angular Acceleration. Angular acceleration = angular velocity over time) this is why the velocity cannot change if torque is zero. Iw = Iw conservation of angular moment says we must conserve it. if we change the moment of inertia we have to change the angular velocity to keep it constant

Nobody at the playground wants to play with an obnoxious boy, so he fashions a seesaw as shown so he can play by himself. Explain how this is done. 1. The fulcrum is very far from the boy. 2. The weight of the boy is balanced with an unknown heavy metal. 3. The weight of the boy is balanced by the weight of the board. 4. The angular velocity of the boy is can- celled with that of the board.

3 Explanation: The weight of the boy is counterbalanced by the weight of the board, which can be considered to be concentrated at its center of gravity on the opposite side of the fulcrum. He is in balance when his weight multiplied by his distance from the fulcrum is equal to the weight of the entire board multiplied by the distance between the fulcrum and the midpoint (center of gravity) of the board.

If you stopped an Earth satellite dead in its tracks, it would simply crash into the Earth. Why, then, don't the communications satellites that hover motionless above the same spot on Earth crash into the Earth? 1. The satellites are not attracted by the Earth. 2. There is no power on the satellites. 3. The satellites' orbital period coincides with the daily rotation of the Earth 4. The moon attracts the satellites at the same time.

3. If the orbital period and direction of motion of an Earth satellite coincide with the daily rotation of the Earth, it is motionless relative to a point on the Earth's surface. Thus the communications satellites actually move at the same pace as the Earth.

A 10,000 N vehicle is stalled one-quarter the way across a bridge. Calculate the additional reaction forces that are supplied at the supports on both ends of the bridge. 1. 6666 N at the left and 3333 N at the right. 2. 9000 N at the left and 1000 N at the right. 3. 8000 N at the left and 2000 N at the right. 4. 7500 N at the left and 2500 N at the right.

4 Let: W=10000N. Let d be the distance from the left end (supporting a weight of F ) and 3 d be the distance from the right end (supporting a weight of f). Since the bridge is in equilibrium, F + f = W F = W - f and D = 3d so, Fd = f(3d) W - f = 3f W = 4f f = W/4 = 2500 N supported at the right and F = W - f = 3/4f = 7500 N supported at the left

What technique would help you to distinguish between two heavy identical-looking spheres of the same weight, one solid and the other hollow? 1. Launch them and compare their trajectories. 2. Hit them and compare their reflective sounds. 3. Plunge them into water and compare their densities. 4. Roll them down an incline and compare their speeds.

4 Explanation: If you roll them down an incline, the solid ball will reach the bottom first. (The hollow ball has more rotational inertia compared with its weight.)

An object has a weight W when it is on the surface of a planet of radius R. What will be the gravitational force on the object after it has been moved to a distance of 4 R from the center of the planet? 1. F = W 2.F =4W 3. F = 1/4 W 4. F = 1/16 W 5. F = 16 W

4 On the surface of the planet, W=GMm. When the object is moved to a distance 4 R from the center of the planet, the gravitational force on it will be F=GMm /(4 R)^2 =GMm /16 R^2 =1/ 16 GMm/ R^2 F = 1/16 W

A uniform plank of length 2 L is balanced at its center of mass. A mother with a mass of 50 kg sits at a distance L/5 from the center of mass and is balanced with her child sitting at the opposite end of the seesaw on the end of the plank. What is the mass of the child? 1. 20 kg 2. 15 kg 3. 5 kg 4. 25 kg 5. 10 kg

5 Let m1 = 50 kg, r1 = L/5 r2 = L In order for the system to be in the static equilibrium, the sum of the torques must be zero, r1m1g = r2m2g so the mass of the child is m2 = (r1/r2)m1 = (1/5) (50 kg) = 10 kg

Because of Earth's rotation about its axis, you weigh slightly less at the equator than at the poles. Why?

Consider one end of a string connected to a spring scale and the other end connected to an object, of true weight w. The tension T in the string will be measured by the scale and construed as the apparent weight. We have w-T=ma. This gives T=w-ma. Thus, the apparent weight is less than the actual weight by the term ma. At the poles the centripetal acceleration is non-zero, and the apparent weight is less than the true weight. you are closer to the sun if at the equators than if at the poles. the r gets slightly smaller. thus the force from the sun pulling on you is greater. this is how it relates to the tension pulling on the block. you have a greater force pulling up on you so your normal force against the earth is lighter.

Tornadoes and hurricanes often lift the roofs of houses. Use the Bernoulli effect to explain why. Why should you keep your windows open under these conditions?

Opening the windows results in a smaller pressure difference between the exterior and interior of the house and, therefore, less tendency for severe damage to the structure due to the Bernoulli effect. What is the Bernoulli effect? as the speed of the gas increases, the pressure decreases because of the pressure difference on the outside is so much lower than the inside of the house the roof with pop off or be lifted. it will explode. just like in space if you went without a space suit you would explode since there is no more pressure acting on you. the pressure on the inside is so much higher, it wants to equilibriate and leave, therefore it will break windows and pop off the roof.

One of the predicted problems due to global warming is that ice in the polar ice caps will melt and raise sea levels everywhere in the world. is that more of a worry for ice (a) at the North Pole, where most of the ice floats on water; (b) at the South Pole, where most of the ice sits on land; (c) both at the North and South Poles equally; or (d) at neither pole?

Rise in water level depends on the amount of water displaced by ice and when it has melted. When it is ice the volume displaced = volume immersed but it s equal to the volume of equal weight of water which always remains same whether it is ice or water. When it is ice it has more volume but that extra volume remains out of water. Since most of the ice in North Pole is sea ice, melting of this ice cannot affect that much of change in sea level. On the other hand, ice stay on land at South Pole. Observable change in sea level occurs due to melting of ice caps at the South Pole, Hence, the correct answer is (B) at the South Pole, where the most of the ice sits on land.

Many people believe that a vacuum created inside a vacuum cleaner causes particles of dirt to be drawn in. Actually, the dirt is pushed in. Explain.

Your moving air in a vacuum cleaner, there is no central "vaccum". a series of fans move air, the moving air pushes the dirt until it is caught by a filter medium which the air is small enough to get through but the dirt is not. The air is then expelled from the device. I guess you could use pistons to move the air as well, but either way your compressing air not pulling air away. In most vacuum cleaners, there is a disk shaped area right next tothe motor. Within the disk are several fans that spin at a veryhigh rate of speed. The blades push air to the outside of the disk.The inside of the disk is left without air and the outside airpressure pushes air into the disk to replace the missing air. So what is essentially happening is the motor is pushing air pressureout of the back of the vacuum so that the outside air pressure willpush into the vacuum hose, bringing the dirt along with it.

Water flows along a streamline down a river of constant width. over a short distance the water slows from speed v to v/3. Which of the following can you correctly conclude about the river's depth? a) It became deeper by a factor of 3 b) It became shallower by a factor of 3 c) It became deeper by a factor of 3^2 d) It became shallower by a factor of 3^2

a A1V2 = A2V2 since we are increasing the area we decrease the velocity

8.6 If global warming continues, it's likely that some ice from the polar ice caps of the Earth will melt and the water will be distributed closer to the equator. If this occurs, would the length of the day (one rotation) a) increase b) decrease c) remain the same

a As more water moves to the center of the earth, the diameter increases. This will increase the radius of the earth, thus increasing the radius in the equation for moment of inertia for a solid sphere. As we increase the radius, we increase the moment of inertia for the earth. Think about the conversation of angular momentum. i1w1 = i2w2 if we rearrange this so that angular velocity 2 is isolated, we get w1(i1/12) = w2. Therefore, as we increase the inertia 2, we decrease the angular velocity 2 since they are indirectly proportionate. This decrease in velocity will slow down the earth's rotation thus increasing the length of the day!

Gravity is an example of a central force that acts along the line connecting two spherical masses. As a planet orbits its sun, (a) how much torque does the sun's gravitational force exert on the planet? (b) What is the change in the planet's orbital angular momentum?

a) zero b) zero

8.4 Two spheres, one hollow and one solid, are rotating with the same angular speed around an axis through their centers. Both spheres have the same mass and radius. Which sphere, if either, has the higher rotational kinetic energy? a) the hollow sphere; b) the solid sphere c) they have the same kinetic energy;

a; A has a greater rotational kinetic energy because it has a larger moment of inertia

8.2 A constant net torque is applied to an object. Which of the following will not be constant? a) angular acceleration b) angular velocity c) moment of inertia d) center of gravity

b ??? net torque is proportional to angular acceleration. but for acceleration to be occurring there must be a change in angular velocity.

9.4 Blood pressure is normally measured with the cuff of the sphygmomanometer around the arm. Suppose the blood pressure is measured with the cuff around the calf of the leg of a standing person. Would the reading of the blood pressure be a) the same here as it is for the arm b) greater than it is for the arm c) less than it is for the arm

b The reason is that gravity increases the likelihood of blood flowing down the body.. i.e it gives blood more energy to go down.. with greater energy/flow of blood there is greater pressure. As a result blood measured at the calf is greater than blood measured at the arm.

7.4 Andrea and Chuck are riding on a merry-go-round. Andrea rides on a horse at the outer rim of the circular platform, twice as far from the center of the circular platform as Chuck, who rides on an inner horse. When the merry-go-round is rotating at a constant angular speed, Andrea's speed is a) twice Chuck's b) the same as Chuck's c) half of Chuck's d) impossible to determine

b the circular angular speed is the same, but the tangential speed is twice as much!

A person in a boat floating in a small pond throws an anchor overboard. What happens to the level of the pond? a) It rises b) It falls c) It remains the same

b why? bouyance when the anchor starts it is in the boat. as it is in the boat it adds weight to the boat which increases displacement of water. therefore it will go up when the anchor is in the boat. once it is thrown overboard it is displacing as much as its volume instead of how much it weighs. its volume is less than its weight because it is more dense than water. therefore, the level of the pond will decrease. Since it is not floating and sinking instead. Displaces more water when it floats. The amount of water it displaces based on its volume when it sinks is a lot less...

7.8 A ball is falling toward the ground. Which of the following statements are false? a) the force that the ball exerts on the Earth is equal in magnitude to the force that Earth exerts on the ball b) the ball undergoes the same acceleration as Earth c) the magnitude of the force the Earth exerts on the ball is greater than the magnitude of the force the ball exerts on the Earth.

b & c; f = ma so mass of the ball x acceleration of the ball = mass of earth x acceleration of earth. therefore the acceleration for the ball is so much greater for the small ball. the force is the same but the ma changes. it has a larger acceleration while it is hitting the earth

Consider an extended object (not a point) with forces F acting on it, producing torques. Is it possible for the situation to exist in which the net force acting on the object (the net force is the sum of all the individual forces acting on the object) is equal to zero, while the net torque about any axis (the net torque is the sum of all the torques acting on the object ) is not equal to zero. a. No b. Yes

b. Yes Explanation: Yes — if the forces are equal and opposite, but do not act along a common line, like pulling the top of a box while pushing the bottom (on the same side), the net force is zero, while the net torque is not!

An object moves in a circular path with constant speed v. Which of the following statements is true concerning the object? a) It's velocity is constant, but its acceleration is changing b) Its acceleration is constant, but its velocity is changing c) Both its velocity and acceleration are changing d) Its velocity and acceleration remain constant

c ; our velocity is changing because it is a vector. its magnitude stays the same. but direction changes. acceleration changes because direction of our acceleration is also changing.

In a tape recorder, the tape is pulled past the read-write heads at a constant speed by the drive mechanism. Consider the reel from which the tape is pulled: As the tape is pulled off, the radius of the roll of remaining tape decreases. (a) How does the torque on the reel change with time? (b) If the tape mechanism is suddenly turned on so that the tape is quickly pulled with a large force, is the tape more likely to break when pulled from a nearly full reel or from a nearly empty reel?

nearly full Explanation: We can assume fairly accurate that the driving motor will run at a constant angular speed and at a constant torque. (a) As the radius of the take-up reel increases, the tension in the tape will decrease, in accordance with the equation: T = T constant/ R take up As the radius of the source reel decreases, given a decreasing tension, the torque in the source reel will decrease even faster, as the following equation shows: T source = TR source = T constant R source / R take up (b) In the case of a sudden jerk on the tape, the changing angular speed of the source reel becomes important. If the source reel is full, then the moment of inertia will be large and the tension in the tape will be large. If the source reel is nearly empty, then the angular acceleration will be large instead. Thus, the tape will be more likely to break when the source reel is nearly full. One sees the same effect in the case of paper towels: It is easier to snap a towel free when the roll is new than when it is nearly empty. the bigger one will break more likely since the moment of inertia is bigger. the r is bigger. the bigger r has a bigger moment of inertia which means it doesn't want to move as much. the tension has to be big enough. you have to pull harder to get it to rotate