Physics 221 Exam 2 Review Questions

A block slides on a track from A to B to C to D. The section from A to B to C is frictionless, but for the section from C to D the coefficient of friction is not zero. Is the block's mechanical (ordered) energy increasing, decreasing, or constant in (a) region AB, (b) region BC, and (c) region CD?

(a) constant (b) constant (c) decreasing

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

(b) (rapid incline to stable on graph)

The radius of the aorta is ~ 10 mm = 10^-2 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 m^2, (ii) 3.75*10^9

A centrifuge in a medical laboratory rotates at an angular speed of 3,600 rev/min. When switched off, it rotates 50 times before coming to rest. What is the constant angular acceleration of the centrifuge?

-226.2/s^2

The boy holds a 40 N weight at arm's length for 10 s. His arm is 1.5 m above the ground. The work done by the force of the boy on the weight while he is holding it is

0

Consider a 100 kg father and his 20 kg girl. They decide to enjoy balancing on a seesaw, which is a uniform board 4 m long and pivoted exactly at its center. If girl sits at the seesaw's end (2m from the center), how far from the center on the other side should the father sit?

0.4 m

Suppose the flow rate of blood in a coronary artery has been reduced to 0.645 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? Enter a number with three digits behind the decimal point.

0.896

How much work (in J) must a person do to lift 5 bundles of shingles each weighing 14 pounds 12 feet onto a roof? 1 pound= 4.448 N, 1 foot= 0.305m Enter an integer. Round up or down correctly

1,140

A car engine delivers 2.2*10^4 W to its wheels when moving at a constant speed of 12.9 m/s. What is the magnitude of the resistive force (in N) acting on the automobile at that speed? Enter an integer.

1,705

Two masses are located on the x-axis. Mass m1= 4 kg is located at x= -50 cm and mass m2= 6 kg is located at x = 20 cm. What is the moment of inertia of the system about the z-axis in units of kgm^2.

1.24

A motor is used to lift and object weighing 15 N a distance of 2 m in 3 seconds. Assuming no conversion of ordered into thermal energy, what is the power output of the motor?

10 W

You live in an apartment directly above an open-air tavern and you possess a really, really long and sturdy straw. You plan to steal beer by leaning out of your apartment window and, when the beer-drinkers are not looking, sticking your straw into beer glasses and sucking on the straw. Assuming you can create a perfect vacuum when you suck on the straw, for this plan to have the chance of working, the height difference between you and the beer must be less than approximately what distance? (Assume the density of beer is equal to the density of water and the pressure is 1 atm= 101 kPa.)

10 m

A 500 N weight sits on the small piston of a hydraulic machine in equilibrium. The small piston has area 2.0 cm^2. If the large piston has area 40 cm^2, how much weight does the large piston support?

10,000 N

A 24 kg object is placed on a 182 cm^2 platform. What is the pressure the object exerts on the platform in N/m^2? Let g= 9.8 m/s^2. Enter an integer.

12,923

Assume g=10 m/s^2. A football's mass is 0.45 kg. If you did the 60 J of work on the football, while throwing it straight up, how high would it go?

13.3 m

Two blocks of mass M and 3 M 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 1200 kg car's speed changes from 5 m/s to 20 m/s in 4 s. By what factor does its kinetic energy change during those 4 s.

16

Suppose you are changing a car tire and loosening a lug nut. You weigh 800 N and stand on the end of a horizontal 2 m long wrench. How much torque do you exert on the lug nut?

1600 Nm

A wheel with moment of inertia 0.09 kgm^2 rotates about a fixed axis. Its kinetic energy is 1,197 J. What is its angular speed ω in s^-1? Enter an integer.

163

A cheerleader lifts his 50 kg partner three times straight up off the ground a distance of 1.1 m before releasing her. How much work does he do lifting her 3 times? Use g=10 m/s^2.

1650 J

In SI units, what is the change in the magnitude of the momentum of a 1,338 kg car that accelerates uniformly along a straight line from a speed of 5 m/s to a speed of 18 m/s in 9 s? Enter an integer.

17,394

A nozzle with a radius of 0.16 cm is attached to a garden hose with a radius of 1.28 cm. If the speed of the water in the hose is 2.86 m/s, what is the speed of the water in the nozzle in m/s? Enter a number with two digits behind the decimal point.

183.04

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

19.6 N

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 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?

19.7 rad/s

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

Suppose the circumference of a bicycle wheel is 2 m. If it rotates at 1 revolution per second when you are riding the bicycle, then your speed will be

2 m/s

A car engine delivers 3.3 * 10^4 W to its wheels when moving at a constant speed of 15.2 m/s. What is the magnitude of the resistive force (in N) acting on the automobile at that speed? Enter an integer.

2,171

In SI units, what is the magnitude the net force acting ona 1,991 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.

2,559

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.

2.4

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 2.3 kg object has kinetic energy 9,245 J. What is the magnitude of its momentum (in kg m/s)? Enter an integer.

206

Use g=10 m/s^2. A block with a weight of 2 N slides across a flat surface with a speed of 15 m/s. What is the kinetic energy of the block?

22.5 J

Blood is pumped from the heart at a volume flow rate of 5.0 liter/min into the aorta (of radius 1.0 cm). Determine the speed of blood through the aorta.

26.5 cm/s

A 750 kg automobile is travelling horizontally with speed 20.0 m/s. What is the automobile's new speed after an additional 150,000 J of net work has been done on the car?

28.3 m/s

A 44 kg object is placed on a 145 cm^2 platform. What is the pressure the object exerts on the platform in N/m^2? Let g= 9.8 m/s^2. Enter an integer.

29,737

A girl pulling a sled exerts a 20 N force horizontally for 40 s. How much power does she generate while moving the sled 60 m?

30 W

Let g= 9.8 m/s^2. A hydraulic system is used to lift a 92 kg motor in a garage. If the motor sits on a piston of area 0.27 m^2, and a force is applied to a piston of area 94 cm^2, what is the minimum force that must be applied to lift the motor in units of N? Enter a number with one digit behind the decimal point.

31.4

An 2.8 kg object gains height 7.7 m while being accelerated from rest to a final speed of 8.9 m/s by an external force. What was the work (in J) done on the object by this force? Let g= 9.8 m/s^2 Enter an integer.

332

You operate a 120 W light bulb for 1 hour. How much energy did you use? (1 W= 1 J/s)

43,200 J

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

Substance A has a density of 3.0 g/cm^3 and substance B has a density of 4.0 g/cm^3. In order to obtain equal masses of these two substances, the ratio VA/VB of the volume of A to the volume of B has to be equal to

4:3

A 3.1 kg object is brought to a stop from a speed of 2.1 m/s in 0.05 m by a spring system. What is the spring constant k of the spring? Enter an integer. Round up or down correctly.

5,468

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/s^2

A CD spins at 5,500 rpm (revolutions per minute). What is the 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 a radius of 0.5 cm, what pressure does she exert on the floor?

6.2 MPa

The volume flow rate of water through a horizontal pipe is 2.7 m^3/min. Determine the speed of flow (in m/s) at a point where the diameter of the pipe is 9.5 cm. Enter a number with two digits behind the decimal point.

6.35

A boy throws a 0.1 kg ball from a height of 1.2 m to and on the roof of a building 8 m high. What is the potential energy of the ball on the roof relative to its starting point?

6.67 J

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

6/5 m, 4/5 m

The volume flow rate of water through a horizontal pipe is 3.6 m^3/min. Determine the speed of flow (in m/s) at a point where the diameter of the pipe is 17.4 cm. Enter a number with two digits behind the decimal point.

62.64

A centrifuge starts from rest. Its angular acceleration α is constant for 16 s. Its final angular speed is ω= 170 revolutions per second. What is its angular acceleration α in units of s^-2? Enter a number with one digit behind the decimal point.

66.8

You are bored during the summertime when school is not in session and you decide to do an experiment where you compare the properties of water and air. If the density of air is 1.25 kg/m^3 and the density of water is 1000 kg/m^3, what volume of air weighs the same as 1 liter (10^-3 m^3) of water?

800 liters

The diameter of a pipe is tripled while the pressure difference across the pipe remains the same. The volume flow rate of the pipe increases by a factor of

81.

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 and B (a tie), C

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

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

Work, as defined in physics is

A scalar quantity, a positive or negative number with units.

The shape of a droplet of liquid on a surface is due to a combination of

Adhesion and cohesion

The vessels shown below all contain water to the same height. Rank them according to the pressure exerted by the water on the vessel bottoms, least to greatest.

All pressures are the same.

The left tip of a wind turbine blade accelerates upward, as you view it. By the right-hand rule, the torque on the wind turbine is pointing

Away from you.

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.

You need to loosen a very tight bolt. You have one wrench and you exert maximum force. Which configuration shown below gives you maximum chance of success?

C (force going straight up with no angle)

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.

A boat is floating in a lake. Since it is floating the buoyant force acting on the boat must be

Equal to its weight.

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

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 take 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.

Suppose you have two containers with liquid in them. One has a density of 760 kg/m^3 and the other has a density of 910 kg/m^3. If an object floats in one container and sinks in the other, the density of the object

Has a volume between 760 kg/m^3 and 910 kg/m^3

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 direction.

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

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

If a viscous fluid flows steadily in a pipe, the fluid speed

Is least near the pipe wall but increases toward the center.

A child is riding a bike and skids to a stop. What happens to their kinetic energy?

It is converted into thermal energy

A car's speed changes from 20 mph to 60 mph. By what factor does its kinetic energy change?

It will increase by a factor of 9.

Water pours gently from an open hose because it

Lost energy throughout its trip to the hose end

The quantities remain constant in an inelastic collision are

Momentum, but neither kinetic energy nor temperature.

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

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.

Which of the following statements is false?

Plaque deposits 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.

Rockets receive their forward propulsion through

Pushing against the exhaust.

A skater who is spinning and throws her arms out slows down because

She makes her rotational mass or moment of inertia bigger.

Two cars move towards each other on a frictionless road as shown in the sketch below. The two cars collide and immediately come to a standstill. During the collision, the total momentum of the two vehicles will

Stay constant.

If only conservative forces act on a system, the total mechanical energy of the system remains constant.

TRUE

One kilogram of iron (density ~ 7.8 gm/cm^3) and 1 kilogram of aluminum (density ~ 2.7 gm/cm^3) are dropping into a pool. Which is acted on by the largest buoyant force?

The aluminum

Suppose Larissa throws a ball up in the air and it comes back down to the same place she threw it from. Ignore the times when the ball is in contact with her hand, and ignore the air resistance.

The ball has minimum kinetic and maximum potential energy at maximum height

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.

It is correct to say that impulse is equal to

The change in momentum.

An ideal, non-compressible fluid is used in the system of pipes shown below. The cross sectional area of pipe 1 is 4 m^2, that of pipe 2 is 3 m^2, and that of pipe 3 is 2 m^2. 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.

No work is done by gravity on a bowling ball that rolls along a bowling alley because

The force of gravity is perpendicular to the balls velocity

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.

Consider a marble rolling around in a bowl sitting on a table on Earth. Neglect friction. Which of the following statements is true?

The gravitational potential energy of the marble depends on the choice of the reference position for zero potential energy

It is possible for two objects of equal mass to have different moments of inertia about the same axis because

The moment of inertia depends on the total mass and the mass distribution.

If the net work done on an object is negative, which of the following statements must be true?

The object loses kinetic energy

If you dangle two pieces of paper vertically a few inches apart and blow air between them

The papers will move together because the increased velocity reduces the pressure between the papers.

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.

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.

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.

When blood flows into an aneurysm

The speed decreases and the pressure increases.

You throw a ball straight up. Compare the sign of the work done by the force of gravity while the ball goes up with the sign of the work done by gravity while it goes down.

The work done by the force of gravity is negative on the way up and positive on the way down

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.

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 are on a cart, initially at rest on a frictionless, horizontal track. You throw a series of identical balls against a wall that is rigidly mounted to the cart. If the balls are thrown at a steady rate and bounce straight back, is the cart put into motion?

Yes, it starts to move to the left and steadily gains speed.

The SI units for viscosity are

kg/(m-s)