Physics 221 Exam 2

The moment of inertia of a meter stick of length L = 100 cm and mass m = 50 g about a perpendicular axis through its center is mL2/12. Two 65 g masses are attached to the stick, at 35 cm to either side of the center. What is the moment of inertia of the system in units of kg cm2 about the perpendicular axis through the center of the stick? Enter an integer.

(.065)(35)^2 + (.065)(35)^2 = 159.25 (50(100)^2) / 12 = 41666.67 g → 41.67 kg 159.25 + 41.67 kg = 200.92

A 2.9 kg object has kinetic energy 8815 J. What is the magnitude of its momentum (in kg m/s)? Enter an integer.

(2)(2.9)(8815) = 226 kg m/s

A car moving at 9 m/s crashes into a wall and stops in 0.11 s. Calculate the magnitude of the force (in N) the seat belt exerts on a passenger in the car to bring him to a halt. The mass of the passenger is 59 kg. Enter an integer.

(9 m/s) (59 kg) = 4827 (0.11 s)

An object is dropped from rest at t = 0 into a viscous fluid. Which of the following best describes the object's speed as a function of time?

(b)

Two identical carts labeled A and B are initially resting on an air track. The coordinate system for describing the system is shown. The cart on the right, cart B is given a push to the left and is released. The clock is then started. At t = 0, cart B moves in the direction shown with a speed v0. They hit and stick to each other. The graphs below describe some of the variables associated with the motion as a function of time. For the experiment described and for each item in the list below, identify which graph is a possible display of that variable as a function of time assuming a proper scale. "The system" refers to carts A and B together. (i) The momentum of cart A (ii) The momentum of cart B (iii) The total momentum of the system (iv) The total kinetic energy of the system

(i) #1, (ii) #3, (iii) #6, (iv) #2

The radius of the aorta is ~ 10 mm = 10-2 m and the blood flowing through it has a speed ~300 mm/s = 0.3 m/s. A capillary has a radius ~4×10-3 mm = 4×10-6 m, but there are literally billions of them. The average speed of blood through the capillaries is ~ 5×10-4 m/s. (i) Calculate the effective cross sectional area of the capillaries and (ii) The approximate number of capillaries.

(i) 0.188 m2, (ii) 3.75*109

Two carts on an air track are pushed towards each other. Initially, cart 1 moves in the positive x direction and cart 2 moves in the negative x direction. They bounce off each other elastically. The graphs at the right describe some of the variables associated with the motion as a function of time. For the experiment described and for each item in the list below, identify which graph is a possible display of that variable as a function of time. If none apply, choose N (for none). (i) The momentum of cart 1 (ii) The position of cart 1. (iii) The position of cart 2.

(i) D, (ii) B, (iii) N

A centrifuge in a medical laboratory rotates at an angular speed of 3600 rev/min. When switched off, it rotates 50 times before coming to rest. What is the constant angular acceleration of the centrifuge?

-226.2/s2

Blood and water have the same contact angle with glass. The density of blood is 5% higher than that of water. (ρblood = 1.05 ρwater) While you make your capillary action measurements you find that water rises in the same tube a factor 1.69 higher than a blood sample. The surface tension of water at the same temperature is 0.073 N/m. What is the surface tension of the blood sample? HINT: h = 2γcosθ/(ρgr) h1/h2 = (γ1cosθ1ρ2r2)/(γ2cosθ2ρ1r1) Here θ1 = θ2 and r1 = r2. Let substance 1 be water and substance 2 be blood.

0.045 N/m

Blood and water have the same contact angle with glass. The density of blood is 5% higher than that of water. (ρblood= 1.05 ρwater) While you make your capillary action measurements you find that water rises in the same tube a factor 1.69 higher than a blood sample. The surface tension of water at the same temperature is 0.073 N/m. What is the surface tension of the blood sample?

0.045 N/m

A 40 kg child standing on a frozen pond throws a 0.5 kg stone to the east with a speed of 5 m/s. Neglecting friction between the child and the ice, what is the recoil velocity of the child?

0.0625 m/s west

A 5.00 kg mass sliding along a horizontal frictionless surface at 2.00 m/s collides with a 1.00 kg stationary mass. After the collision the two masses stick together and contact a light Hooke's-law spring with spring constant k = 1000 N/m. What is the maximum compression (in m) of the spring?

0.13 m

An intravenous blood plasma drip enters a vein in the patient's arm from a bag raised a height h above the vein. If the diameter of the 5 cm long needle is 0.5 mm, use Poiseuille's law to find the height h that results in a 5 cm3/min flow rate. (Assume the blood pressure in the arm is 18 torr = 2392 Pa and the viscosity of the blood plasma is 1.5*10-3 Pa-s.)

0.66 m

A 90 kg man and a 10 kg girl are initially 10 m apart. They are connected by a massless rope, and are sitting on a frictionless horizontal surface. The man pulls on the rope until they meet. Where do they meet?

1 m away from the initial position of the man.

Angular speed is measured in units of s-1, which is rad/s. How many degrees correspond to 1 radian?

1 rad = 57.3 degrees 1 r = 360*/2πr = 180*/πr = 57.3

When the body requires an increased blood flow rate in a particular organ or muscle, it can accomplish this by increasing the diameter of arterioles on that area. By what factor must the diameter of an arteriole increase to double the volume flow rate of blood, all other factors remaining the same?

1.19

Two fluids have the same contact angle with glass. The density of fluid 1 is larger than the density of fluid 2. (ρ1 = 1.06 ρ2) The surface tension of fluid 1 is larger than that of fluid 2. (γ1 = 1.42 γ2) Find the ratio h1/h2 of the heights to which a liquid will rise through capillary action in the same capillary tube.

1.42/1.06 = 1.34

A water pump generates a constant flow Q, which is causing a turbulent spray (Reynolds number R = 3200) out of this cylindrical nozzle: You want to achieve laminar flow with a Reynolds number below 2000 by picking a different nozzle. Your nozzle should have a diameter

1.6 D or greater.

This pocket watch is keeping perfect time. What is the angular speed ω of its minute hand in units of rad/s?

1.75*10-3 rad/s

A block of plastic material floats in water with 63.3% of its volume under water. What is the density of the block in kg/m3?

1000 * 0.633 * v = ρv ρ = 1000 * 0.633 = 633 kg/m3

The lungs can exert a negative pressure, with respect to atmospheric pressure, of up to 1.3 kPa. To what height can you suck water through a straw? REMEMBER: A 10 m high column of water exerts a pressure of ~100 kPa

13 cm

Two blocks of mass M and 3M are placed on a horizontal frictionless surface. A light spring is attached to one of them, and the blocks are pushed together with the spring between them. A cord holding them together is burned, after which the block of mass 3 M moves to the right with a speed of 5 m/s. What is the speed of the block of mass M?

15 m/s to the left.

A wheel with moment of inertia 0.07 kgm2 rotates about a fixed axis. Its kinetic energy is 1850 J. What is its angular speed, ω, in s-1? Enter an integer.

1850 J = (½) (.07) (ω2) ω = SQRT(1850/.035) ω = 229.91

A 2 kg block of wood is floating in water. What is the magnitude of the buoyant force acting on the block?

19.6 N

A 1 kg rock is suspended by a massless string from one end of a meter stick at the 0 cm mark. What is the mass m suspended from the meter stick at the 75 cm mark if the system is balanced?

2 kg

Both the disk and the ring have the same mass, and the same radius. Which has the larger moment of inertia about the center? HINT: The farther the bulk of the mass of an object is from an axis, the larger is the moment of inertia of the object about this axis.

2) The ring

A fan rotating with an initial angular velocity of 1000 rev/min is switched off. In 2 seconds, the angular velocity decreases to 200 rev/min. Assuming the angular acceleration is constant, how many revolutions does the blade undergo during this time?

20

A 104 N car is lifted by a manually operated hydraulic lift. The area of the shaft of the lift is 80 cm2; the area of the piston that forces liquid into the system is 2 cm2. What minimum force must be exerted on this piston to lift the car?

250 N

A block of wood of uniform density floats so that exactly 1⁄4 of its volume is underwater. What is the density of the block?

250 kg/m3

A centrifuge starts from rest. Its angular acceleration, α, is constant for 18 s. Its final angular speed is ω = 381 revolutions per second. What is its angular acceleration α in units of s-2? Enter a number with one digit behind the decimal point

381*2π= 2393.89 radians=ω ω/s 2393.89/18s = 133

Mercury has an unusually large surface tension γ = 0.465 N/m. Calculate the excess pressure inside a drop of mercury 4 mm in diameter.

465 Pa

An object rotates initially with a period of 1.0 s. It accelerates with constant angular acceleration for 10 s. Its final rotation period is 0.1 s. What was the magnitude of its angular acceleration?

5.65 rad/s2

A 50 g meter stick lies on the x-axis with its left edge (the 0 cm mark) at the origin. A 56 g mass is attached to the stick at x = 80 cm and a 12 g mass is attached at x = 10 cm. Find the x-coordinate of the center of mass of the system in cm. Enter a number with one digit after the decimal point.

50 (50) + 56 (80) + 12 (10) = 60.2 50 + 56 + 12

You can chew through very tough objects with your incisors because they exert a large force on the small area of a pointed tooth. What pressure in MPa can you create by exerting a force of 500 N with your tooth on an area of 1.00 mm2? Enter an integer.

500

A beaker containing 5.0 kg of water is on a weighing scale. A 0.8 kg block of metal that has density 8*103 kg/m3 that is attached to a string is lowered completely into water without touching the bottom. Assume that the beaker is massless, and water has density 103 kg/m3, and g = 10 m/s2. What is the reading on the scale?

51 N

A CD spins at 5500 rpm (revolutions per minute). What is its angular speed in units of rad/s or s-1?

576

A 50 kg woman balances on one heel of a high-heel shoe. If the heel is circular with radius 0.5 cm, what pressure does she exert on the floor?

6.2 MPa

A horizontal pipe, 10 cm in diameter, has a smooth reduction to a pipe 5 cm in diameter. If the pressure of the water in the larger pipe is 8.00*104 Pa and the pressure in the smaller pipe is 6.00*104 Pa, what is the flow speed of the water (in m/s) in the smaller pipe?

6.53 m/s

A 2 kg mass is at x = 0 m, y = 2 m, and a 3 kg mass is at x = 2 m, y = 0 m. The x- and y-coordinates, respectively, of the center of mass of this system are

6/5 m, 4/5 m

A soap bubble with radius of 3.0 cm is floating in air. What is the pressure difference across the two surfaces of the bubble? The surface tension of soapy water is γ = 69 * 10-3 N/m.

9.2 N/m2

A certain pump can exert a negative gauge pressure of 9.3 kPa. It is used to suck a liquid out of a bucket up a thin pipe. An 8.9 m column of the liquid exerts a pressure of 100 kPa. To what maximum height (in m) can the liquid be sucked up the pipe by this pump?

9.3 kPa/x = 100 kPa/8.9 m 82.77 = 100x x = .83 m

A steel bridge is built in several segments, each 20 m long. The gap between segments is 2 cm at 18 oC. What is the maximum temperature that the bridge can manage before buckling? α(steel) = 13*10-6 /(oC) HINT: ΔL = α L ΔT)

95 degrees Celsius

Three forces labeled A, B, C are applied to a rod, which pivots on an axis through its center. Which force produces the torque with the largest magnitude about this axis? HINT: magnitude: τ = r F sinθ r = vector pointing from axis of rotation to point where force F is applied. θ = smallest angle between r and F.

A

Fluid is flowing from left to right through the pipe. Points A and B are at the same height, but the cross-sectional areas of the pipe differ. Points B and C are at different heights, but the cross-sectional areas are the same. Rank the pressures at the three points, from highest to lowest.

A, B, C

A nozzle with a radius of 0.21 cm is attached to a garden hose with a radius of 1.18 cm. If the speed of the water in the hose is 1.20 m/s, what is the speed of the water in the nozzle in m/s?

A1 V1 = A2 V2 V1 = (r2 / r1)2 * V2 V1 = (1.18 cm / 0.21 cm)2 * (1.20 m/s) V1 = 37.888 m/s

Consider two carts, of masses m and 2m, at rest on an air track. You push on each cart for 3 s, exerting equal force Fnet on each.

After the push, the momentum of mass m is the same as the momentum of mass 2m.

Consider three drinking glasses. All three have the same area base, and all three are filled to the same depth with water. Glass A is wider at the top than at the bottom, glass B is cylindrical and holds less water than A. Glass C is narrower at the top than at the bottom, and so holds less water than B. Which glass has the greatest liquid pressure at the bottom?

All three have equal pressure at the bottom.

Water with air bubbles flows through a pipe that becomes narrower. Compared to the wider region, the bubbles in the narrow region are

Bigger

The picture below shows 5 blocks. The blocks have equal volumes but different masses. The blocks are placed in an aquarium tank filled with water and blocks 2 and 5 come to rest as shown in the figure. Which answer is correct?

Block 3 will come to rest in the same position as block 5.

Two objects, A and B, have the same volume and are completely submerged in a liquid, although A is deeper than B. Which object, if either, experiences the greater buoyant force?

Both objects experience the same buoyant force.

A disk is spinning with angular velocity ω as shown. It begins to speed up. While it is speeding up, what are the (i) directions of its angular velocity, ω (ii) and its angular acceleration, α **Angular acceleration does not necessarily point in the direction of the angular velocity. For a fixed rotation axis, it points in the direction of ω if the rotation rate is increasing and opposite to the direction of ω if the rotation rate is decreasing.

C, C

In an experiment, water rose by capillary attraction through two columns of soils: one with coarse grains (column 1) and the other with fine grains (column 2). In which column did the water rise to greater height?

Column 2

When water flows smoothly in a straight hose, its viscosity causes the water to

Convert some of its kinetic energy into thermal energy.

An object moves with constant speed in the clockwise direction along the circular path shown below. At the point indicated by the black dot, in which direction is the angular velocity vector, ω, pointing?

D - into the paper

Let g = 9.8 m/s2. A hydraulic system is used to lift a 81 kg motor in a garage. If the motor sits on a piston of area 0.38 m2, and a force is applied to a piston of area 93 cm2, what is the minimum force that must be applied to lift the motor in units of N?

F = (0.0093/.38) * (9.8)(81) F = 19.4 N

Modeling a meter stick as a forearm, compare the force FB that the biceps has to exert to keep the forearm horizontal to the weight of the forearm FW = mg. Let d = 10 cm and the distance from where the biceps muscle attached to the center of mass be d' = 40 cm.

FB = 5 mg

Referring to the graph below, which phase has the smallest specific heat capacity?

Gas

In soap box car races, the cars are boxes with wheels. They begin at rest at the top of a hill, and at the start of the race they all begin rolling down the hill. The soap box car that reaches the bottom of the hill first is the winner. You have entered a soap box car race where the rule is that all the wheels and cars must have equal mass. Since you have taken Physics, you know that it is worse to have wheels with spokes (where the mass is mostly on the rim) rather than solid wheels because

Given the same torque, the wheels with spokes have a higher rotational mass or moment of inertia and therefore will have a smaller angular acceleration.

During a football game the ball is kicked and it travels across the field. If the ball is kicked away from its center of mass it will

Have translational and rotational motion.

A man, with his arms at his sides, is spinning on a light, frictionless turntable. When he extends his arms

His angular momentum remains the same

Flowing honey is less likely to become turbulent than flowing water because

Honey's large viscosity favors laminar flow.

A person sips a drink through a straw. At which of the following three positions is the pressure lowest?

I. Inside the person's mouth

Consider two masses, each of size 2m at the ends of a light rod of length L with the axis of rotation through the center of the rod. The rod is doubled in length and the masses are halved. Compare IA and IB.

IA < IB

Orange growers in Florida spray their trees with water when they expect a freeze. Why does this work?

If a mixed phase of water and ice is present, the temperature does not drop below 0˚C.

Consider a block of wood floating on water. If you push down on the top of the block until it is completely submerged, the buoyant force on it

Increases

Suppose you are riding on a merry - go - round and you move out to the edge. What happens to the rotational rate of the system?

It decreases because angular momentum is conserved and the moment of inertia increases.

If the absolute temperature of a gas is halved, what happens to the average (root-mean-square or RMS) speed, √<v2>, of the gas molecules?

It decreases to 1/√2 the original average speed.

Blood is called a complex fluid because

Its viscosity depends on the velocity of the flow.

The fundamental dimensions of pressure are

M L-1 T-2

Consider the earth spinning from west to east on its axis. It is slowing down in its rotation due to friction with the air. Using the right hand rule, in what direction is the frictional torque?

N pole to S pole

An ice-cube sits in a bath of water. The water, the ice and the surrounding air are all at 0˚C. Does heat enter the ice cube?

No

Two moving objects have masses m1 and m2, respectively. If m2 = 4m1, and both have the same kinetic energy, which has more momentum?

Object 2 with mass m2.

A 13 kg object is placed on a 106 cm2 platform. What is the pressure the object exerts on the platform in N/m2? Let g = 9.8 m/s2.

P = F/A F = ma = (13)(9.8) = 127.4 (127.4)/(0.0106) = P P = 12019 N/m2

A 500 N weight sits on the small piston of a hydraulic machine in equilibrium. The small piston has area 2.0 cm2. If the large piston has area 40 cm2, how much weight does the large piston support?

P=FA P1=P2 F1/A1= F2/A2 500 N/ 2.0 cm2 = F2/ 40 cm2 F2 = 40/2.0 cm2 * 500 N F2 = 10,000

Which of the following statements is false?

Plaque deposit on an artery or arteriole wall causes an increase in local blood pressure and can lead to bursting of that vessel.

A DVD is rotating with an ever-increasing speed. How do the angular velocity, angular acceleration, tangential velocity, and tangential acceleration compare at points P and Q?

Points P and Q have the same angular velocity and the same angular acceleration.

In a stationary homogeneous liquid near the surface of Earth, which of the following is true?

Pressure is the same at all points at the same height.

A 0.6 kg toy car moving in the positive x direction with speed 2.3 m/s hits a toy car of equal mass moving in the positive y-direction with speed of 4.1 m/s. If the collision is perfectly inelastic, calculate the speed of the cars (in m/s) right after the collision. Enter a number with one digit after the decimal point.

Px = mvx = (0.6 kg)(2.3 m/s) = 1.38 Py = mvy = (0.6 kg)(4.1 m/s) = 2.46 P = (Px)2 + (Py)2= (1.38)2+(2.46)2 = 2.8206/(2*0.6 kg) = 2.4 m/s

Suppose the flow rate of blood in a coronary artery has been reduced to 0.616 times its normal value by plaque deposits, and that the pressure difference across the artery has not changes. By what factor has the radius of the artery been reduced, assuming no turbulence occurs?

Q2 = 0.616 Q1 r2 = 0.616 r1 0.6160.25 = 0.886

People fighting forest fires carry emergency tents that have shiny aluminum outer surfaces. If there is trouble, a firefighter can lie under the tent to block the heat from burning trees overhead. The tent helps because

Radiation carries heat downward toward the fire fighter and the aluminum tent reflects most of that radiation.

Detergents or wetting agents

Reduce the angle of contact.

In the constellation Orion, you can easily observe the difference between the reddish looking star Betelgeuse and the bluish looking star Rigel. Which of the two has the hotter surface temperature?

Rigel

Consider a rod of uniform density with an axis of rotation through its center and an identical rod with the axis of rotation through one end. Which has the larger moment of inertia about its axis of rotation?

Rod B with the axis through one end.

On a humid summer day, perspiration does not cool you off much. Why?

The air is almost saturated with water vapor and there is almost no net evaporation.

One kilogram of iron (density ~7.8 gm/cm3) and 1 kilogram of aluminum (density ~2.7 gm/cm3) are dropped into a pool. Which is acted on by the largest buoyant force?

The aluminum

Some children are riding on the outside edge of a merry-go-round. Ignore friction in the rotation of the merry-go- round. Consider the "system" of the children plus the merry-go-round. At the same time, the children all move towards the center of the merry-go- round. When they do this

The angular momentum of the system stays constant.

A block and a rod are joined together. Each object is of uniform density. The center of mass of the combined object is at the position shown by the "X." Which has the greater mass, the block or the rod?

The block has the greater mass.

You can balance a broom on your hand if you're careful. To do this trick well, you must look at

The broom's center of gravity.

When you sit facing a campfire outdoors, your face feels quite warm because

The campfire is radiating heat towards your skin

Determine the character of the collision. The masses of the blocks, and the velocities before and after are given.

The collision is not possible because momentum is not conserved.

A bass has a gas-filled sac or air bladder that allows it to float motionless below the surface of the water. What is the bass's average density?

The density of water.

Compare the flight of two golf balls given the same impulse by the club. Which ball will travel a larger distance?

The dimpled ball.

Assume a disk and a ring with the same radius roll down an incline of height h and angle theta. If they both start from rest at t = 0, which one will reach the bottom first?

The disk

An ideal, non-compressible fluid is used in the system of pipes shown below. The cross sectional area of pipe 1 is 4 m2, that of pipe 2 is 3 m2, and that of pipe 3 is 2 m2. The fluid enters pipe 1 at 2 m/s, and leaves pipe 2 at 3 m/s. What is the speed of the fluid in pipe 3 and in which direction does it flow?

The fluid leaves pipe 3 (downward) with speed 0.5 m/s.

A sphere, a hoop, and a cylinder, all with the same mass M and the same radius R, are rolling along, all with the same speed v. Which has the most total kinetic energy? HINT: The farther the bulk of the mass of an object is from an axis, the larger is the moment of inertia of the object about this axis.

The hoop

A chair has a wooden seat but metal legs. The chair legs feel colder to the touch than does the seat. Why?

The metal has a higher thermal conductivity than the wood.

Blood flows through a section of a horizontal artery that is partially blocked by a deposit along the artery wall. A hemoglobin molecule moves from the narrow region into the wider region. What happens to the pressure acting on the molecule as it moves from the wider into the narrower region?

The pressure decreases.

Suppose that there is a partial blockage of the aorta, which normally pumps about 5 L of blood per minute. If the diameter of the aorta were reduced by 30%, what increase in blood pressure gradient would be needed to obtain the normal flow rate? (Assume that Poiseuille's law applies.)

The pressure gradient would have to increase by a factor of 4.2.

Blood flows through a section of a horizontal artery that is partially blocked by a deposit along the artery wall. A hemoglobin molecule moves from the narrow region into the wider region. What happens to the pressure acting on the molecule as it moves from the narrow to the wider region?

The pressure increases.

Compared to a gear tooth on the rear sprocket (on the left, of small radius) of a bicycle, a gear tooth on the front sprocket (on the right, of large radius) has

The same linear speed and a slower angular speed.

Two bubbles are connected by a hollow tube plus a valve. What will happen once the valve between the two is opened? REMEMBER: The smaller a soap bubble, the higher the pressure inside.

The small bubble will drain into the big bubble.

When blood flows into an aneurysm

The speed decreases and the pressure increases.

During a July 4th firecracker party, a pop bottle rocket lying still on the ground explodes, sending fragments everywhere. If the momentum of the pop bottle rocket (ignore friction!) initially at rest is conserved during an explosion, what can be said about the kinetic energy of various fragments after the collision?

The total kinetic energy afterwards is greater than what it was initially.

In your dorm room you watch the Vols play in an out-of-town game. It is a cliffhangers and the winner will be determined in the last few seconds of play. Everybody is taking their bathroom break right after the game ends. As the toilets flush and hands are washed, the faucet pressure is noticeably reduced, even though the supply pipe to the rooms can carry all the water needed. Why?

The water has to speed up in the supply pipe; therefore, the pressure drops in the pipe.

Which of the following assumptions is not made in the derivation of Bernoulli's equation?

There is negligible gravity.

Why do elastic balls bounce so well?

They store energy through compression, like a spring.

Why can't you get all the dust off your car by just squirting water from a hose onto it? Why can't you simply remove dust just by blowing across a surface? Why does dust cling to a fast rotating fan? How can a leaf stay on a car moving at high speed? What is one common answer to all these questions?

This is a consequence of the formation of stationary Boundary Layer.

A boat floating in a lake contains a block of volume V0. The density of the block is 5000 kg/m3. If the block is thrown overboard, the volume of the water displaced by the block is

V0

The four things that affect the amount of water flowing through a hose are

Water viscosity, hose length, inlet and outlet pressure difference, hose diameter

Your dryer is broken, so you have to hang your wet clothes from the washing machine outside to dry. Under which conditions would your clothes dry fastest?

When it is 75˚F with 50% relative humidity.

A man jumps off of a bridge towards a river below. As he falls, he feels himself spinning forward (clockwise in diagram). To keep from hitting the water head-first, the man should

Windmill his arms clockwise to keep upright

In SI units, what is the magnitude the net force acting on a 1991 kg car that accelerates uniformly along a straight line from a speed of 8 m/s to a speed of 17 m/s in 7 s? Enter an integer.

a = (vf - vi)/∆t = (17-8)/7 = 9/7 = 1.2857 1.2857 * 199a kg = 2560

Suppose you work in the E.R. and a choking patient comes in with their trachea half obstructed. (The diameter is half of what it was before the obstruction.) You manage to correct the problem and send them on their way safely, explaining that such obstructions are particularly dangerous because HINT: Q = π∆Pr4/(8ηL) Q α r4

a half - blocked airway passes only 1/16 the regular amount of air.

Calculate the gauge pressure (in Pa) inside a soap bubble 3.2 cm in radius using the surface tension γ = 0.037 N/m for the solution.

gauge pressure = 4γ / (r * 10-2) = (4)(0.037)(3.2 * 10-2)= 4.6 Pa

A drum major is given two batons, one gold and one plastic. He is told that both batons have the same mass. He tries spinning each one and finds that the plastic one is much easier to start and stop spinning. He correctly concludes that the plastic baton, in comparison to the gold baton

has more of its mass distributed towards the center.

In SI units, what is the change in the magnitude of the momentum of a 1196 kg car that accelerates uniformly along a straight line from a speed of 9 m/s to a speed of 16 m/s in 6 s? Enter an integer.

i = (1996 kg)(9 m/s) = 10764 f = (1996 kg)(16 m/s) = 19136 19136 - 10764 = 8372

The SI units for viscosity are:

kg/(m-s)

Rockets receive their forward propulsion through

pushing against the exhaust.

Dimples on a golf ball hit without spin

reduce drag.

It is correct to say that impulse is equal to:

the change in momentum

After clearing the bar on a high jump, you land softly on a giant mattress. Landing on a mattress is more comfortable than landing on a sand heap of equal size because

the force the mattress exerts on you to stop your descend is much less than the force the sand heap would exert on you.

A beaker is filled with water to the rim. Gently you place a toy duck in the beaker and some of the water spills out. The duck floats. The weight of the beaker with the duck floating in it is

the same as its weight before adding the duck.

Suppose you have an aquarium. You have a solid plastic decoration and a rock of about the same volume but the rock has twice the mass. Both are totally submerged in the water. The buoyant force on the plastic object is about

the same as that on the rock.

A scuba diver descends to a depth of 20 m. At that depth, the pressure is approximately

three times atmospheric pressure

A bicycle's wheels have a radius of 33 cm. The bicycle is traveling at a speed of 6.5 m/s. What is the angular speed of the front tire?

v=wr w=v/r v=6.5 r=33 cm= .33 m 6.5/.33 m= 19.7 radian/sec

For a smooth sphere with a 12 cm diameter thrown through air (air density of 1.25 kg/m3, air viscosity 1.83*10-5 Pa-s), what is the speed (in cm/s) when the Reynolds number is 4036?

velocity = ((4036)(1.83 * 10-5))/((1.25)(12/100)) X 100 = 49.2 cm/s

Two carts A and B are moving towards each other as shown in the diagram. They collide and come to rest at the point of impact. From this observation we can conclude that the carts

were moving with momenta equal in magnitude and opposite in direction.

Suppose you have a very long straw that can reach from a cup of water on the ground level to the top of a very tall building. When you use a pump to suck on the straw in order to bring water up,

you can bring the water up to only a maximum height in the straw, when the pressure of the water column is approximately equal to the atmospheric pressure.

The graph shows the acceleration of a cart with mass m = 0.555 kg, moving initially with constant speed, as a function of time, as a force F = ma stops the cart. Estimate the initial momentum of the cart in units of kg m/s.

~ 0.6

A wheel starts from rest with constant angular acceleration, α. It requires 3.1 s to make 40 revolutions. What is its angular acceleration, α, in s-2? Enter a number with one digit behind the decimal point.

ϴ = ωinitial + ½ acceleration * t2 ϴ = (40)(2π) → 80π 80π = 0 + ½ α (3.1)2 α = 52.3 s-2