Test 3: Chapter 7, 8 & 9

A mechanic is examining the wheel of a bicycle to adjust the brake. With the bicycle off the ground, he manually rotates the wheel until it reaches an angular speed of 12.0 rad/s and then allows it to coast to a stop. If the wheel has a moment of inertia of 0.100 kg m2, and the wheel slows uniformly to a stop in 160 s, what is the magnitude of the retarding torque? a. 1.00 N m b. 0.00750 N m c. 0.0787 N m d. 1.33 N m e. 1.67 N m

0.00750 N m

A small ball is tied to one end of a light 2.5-m wire, and the other end of the wire is hooked to the ceiling. A person pulls the ball to the side until the wire makes an angle of 35° with the plane of the ceiling and then gently releases it. What is the angular speed of the ball, in rad/s, as it swings through its lowest point?

1.83 rad/s

A string is wrapped tightly around a fixed pulley that has a moment of inertia of 0.0352 kg m2 and a radius of 12.5 cm. A mass of 423 g is attached to the free end of the string. With the string vertical and taut, the mass is gently released so it can descend under the influence of gravity. As the mass descends, the string unwinds and causes the pulley to rotate, but does not slip on the pulley. What is the speed of the mass after it has fallen through 1.25 m? a. 2.00 m/s b. 2.28 m/s c. 1.97 m/s d. 3.94 m/s e. 4.95 m/s

1.97 m/s

A cylinder of radius 8.0 cm rolls 20 cm in 5.0 s without slipping. Through how many degrees does the cylinder turn during this time?

143 degrees

Express the angular speed of an old 33 1/3 rpm LP in rad/s.

3.49 rad/s

A 50-g ball moving at 10 m/s in the +x direction suddenly collides head-on with a stationary ball of mass 100 g. If the collision is perfectly elastic, what is the velocity of each ball immediately after the collision? a. -3.3 m/s, +6.7 m/s b. +3.3 m/s, -6.7 m/s c. -6.7 m/s, +3.3 m/s d. +6.7 m/s, -3.3 m/s

a. -3.3 m/s, +6.7 m/s

What is the kinetic energy of a 120-cm thin uniform rod with a mass of 450 g that is rotating about its center at 3.60 rad/s? a. 0.350 J b. 4.20 J c. 0.700 J d. 0.960 J e. 2.10 J

a. 0.350 J

A 15-kg child is sitting on a playground teeter-totter, 1.5 m from the pivot. What is the minimum distance, on the other side of the pivot, such that a 220-N force will make the child lift off the ground? a. 1.0 m b. 1.5 m c. 0.10 m d. 9.8 m e. 2.4 m

a. 1.0 m

A string is wound tightly around a fixed pulley having a radius of 5.0 cm. As the string is pulled, the pulley rotates without any slipping of the string. What is the angular speed of the pulley when the string is moving at 5.0 m/s? a. 100 rad/s b. 50 rad/s c. 25 rad/s d. 20 rad/s e. 10 rad/s

a. 100 rad/s

A meter stick balances at the 50.0-cm mark. If a mass of 50.0 g is placed at the 90.0-cm mark, the stick balances at the 61.3-cm mark. What is the mass of the meter stick? a. 127 g b. 178 g c. 89.7 g d. 32.6 g e. 73.4 g

a. 127 g

A wheel accelerates from rest to 59 rad/s at a uniform rate of 58 rad/s Through what angle (in radians) did the wheel turn while accelerating? a. 30 rad b. 24 rad c. 60 rad d. 38 rad

a. 30 rad

A block of mass m = 34 kg and speed V is behind a block of mass M = 81 kg and speed of as shown in the figure. The surface is frictionless and the blocks collide and couple. After the collision, the blocks have a common speed of What is the magnitude of the impulse on the 34-kg block due to the collision? a. 32 N s b. 14 N s c. 41 N s d. 57 N s e. 73 N s

a. 32 N*s

A light-weight potter's wheel, having a moment of inertia of 24 kg*m^2 is spinning freely at 40.0 rpm. The potter drops a small but dense lump of clay onto the wheel, where it sticks a distance 1.2 m from the rotational axis. If the subsequent angular speed of the wheel and clay is 32 rpm, what is the mass of the clay? a. 4.2 kg b. 2.8 kg d. 3.7 kg e. 4.6 kg

a. 4.2 kg

A vertical 30-cm steel rod, 1.0 cm in diameter, supports a 300-kg mass. What is the change in length of the rod caused by this mass? Young's modulus for steel is 2.0 × 1011 N/m2. a. 5.6 × 10-5 m b. 6.5 × 10-5 m c. 5.6 × 10-6 m d. 6.5 × 10-6 m e. 6.5 × 10-4 m

a. 5.6 × 10-5 m

An irregularly shaped object that is 10 m long is placed with each end on a scale. If the scale on the right reads 96 N while the scale on the left reads 71 N how far from the left end is the center of gravity of this object? a. 5.7 m b. 7.4 m c. 4.3 m e. 14 m

a. 5.7 m

Calculate the impulse due to a force of that lasts for a. 6.3 kg m/s b. 5.0 kg m/s c. 5.7 kg m/s d. 6.9 kg m/s

a. 6.3 kg m/s

Through how many degrees does a 33 rpm turntable rotate in a. 63° b. 35° c. 46° d. 74°

a. 63°

A 5-kg ball collides inelastically head-on with a 10-kg ball, which is initially stationary. Which of the following statements is true? (There could be more than one correct choice.) a. The magnitude of the change of velocity the 5-kg ball experiences is greater than that of the 10-kg ball. b. The magnitude of the change of velocity the 5-kg ball experiences is less than that of the 10-kg ball. c. The magnitude of the change of velocity the 5-kg ball experiences is equal to that of the 10-kg ball. d. The magnitude of the change of velocity the 5-kg ball experiences is greater than that of the 10-kg ball. e. Both balls lose all their momentum since the collision is inelastic.

a. The magnitude of the change of velocity the 5-kg ball experiences is greater than that of the 10-kg ball. d. The magnitude of the change of velocity the 5-kg ball experiences is greater than that of the 10-kg ball.

Which one of the following is an accurate statement? a. The ratio of tensile stress to tensile strain is called Young's modulus. b. "Strain" has a meaning very close to "force." c. "Stress" has a meaning very close to "stretch." d. Tensile stress is measured in newtons. e. Tensile strain is measured in meters.

a. The ratio of tensile stress to tensile strain is called Young's modulus.

Three cars, car X, car Y, and car Z, begin accelerating from rest at the same time. Car X is more massive than car Y, which is more massive than car Z. The net accelerating force exerted on each car is identical. After 10 seconds, which car has the most amount of momentum? a. They all have the same amount of momentum. b. Car X c. Car Y d. Car Z

a. They all have the same amount of momentum.

A 0.14-kg baseball is dropped from rest from a height of 2.0 m above the ground. What is the magnitude of its momentum just before it hits the ground if we neglect air resistance? a. 0.28 kg m/s b. 0.88 kg m/s c. 0.44 kg m/s d. 0.62 kg m/s e. 1.4 kg m/s

b. 0.88 kg*m/s

A rolling wheel of diameter of 68 cm slows down uniformly from 8.4 m/s to rest over a distance of 115 m. What is the magnitude of its angular acceleration if there was no slipping? a. 1.8 rad/s2 b. 0.90 rad/s2 c. 5.7 rad/s2 d. 11 rad/s2

b. 0.90 rad/s2

Opposing shearing forces of 3000 N are applied to the 4.00-cm × 5.00-cm faces of a metal block measuring 3.00 cm × 4.00 cm × 5.00 cm. By what amount does the block become slanted? The shear modulus for this metal is 8.10 × 1010 N/m2. a. 1.54 × 10-6 m b. 5.56 × 10-7 m c. 9.88 × 10-7 m d. 3.08 × 10-6 m e. 6.98 × 10-6 m

b. 5.56 × 10-7 m

A golf ball of mass 0.050 kg is at rest on the tee. Just after being struck, it has a velocity of 102 m/s. If the club and ball were in contact for 0.81 ms, what is the average force exerted on the ball by the club? a. 5.5 kN b. 6.3 kN c. 4.9 kN d. 7.1 kN

b. 6.3 kN

Consider a uniform hoop of radius R and mass M rolling without slipping. Which is larger, its translational kinetic energy or its rotational kinetic energy? a. Translational kinetic energy is larger. b. Both are equal. c. Rotational kinetic energy is larger. d. You need to know the speed of the hoop to tell.

b. Both are equal.

If the sum of the external forces on an object is zero, then the sum of the external torques on it must also be zero. a. True b. False

b. False

If the sum of the external torques on an object is zero, then the sum of the external forces on it must also be zero. a. True b. False

b. False

There must be equal amounts of mass on both sides of the center of mass (or center of gravity) of a system. a. True b. False

b. False

A piece of iron sinks to the bottom of a lake where the pressure is 21 times what it is at the surface of the lake. Which statement best describes what happens to the volume of that piece of iron? a. There has been no change in the volume of the iron. b. Its volume decreases slightly. c. Its volume increases slightly. d. Its volume becomes 21 times greater than at the surface. e. Its volume becomes 1/21 what it was at the surface.

b. Its volume decreases slightly.

A croquet mallet balances when suspended from its center of mass, as shown in the left part of the figure. If you cut the mallet into two pieces at its center of mass, as shown in the right part of the figure, how do the masses of the two pieces compare? (There could be more than one correct choice.) a. The masses are equal. b. The piece with the head of the mallet has the greater mass. c. The piece with the head of the mallet has the smaller mass. d. It is impossible to tell.

b. The piece with the head of the mallet has the greater mass. d. It is impossible to tell.

The graph in the figure shows the tensile stress as a function of the tensile strain in a certain wire. What does the slope of this graph give us for this wire? a. the pressure in the wire b. Young's modulus for the material of the wire c. the tensile stress in the wire d. the tension in the wire e. the percent change in the length of the wire

b. Young's modulus for the material of the wire

A uniform solid cylinder of mass 10 kg can rotate about a frictionless axle through its center O, as shown in the cross-sectional view in the figure. A rope wrapped around the outer radius R1 = 1.0 m exerts a force of magnitude F1 = 5.0 N to the right. A second rope wrapped around another section of radius R2 = 0.50 m exerts a force of magnitude F2 = 6.0 N downward. What is the angular acceleration of the cylinder? a. 1.0 rad/s2 b. 0.60 rad/s2 c. 0.40 rad/s2 d. 0.80 rad/s2

c. 0.40 rad/s2

A 25-kg television set rests on four rubber pads, each one having a height of 1.0 cm and a radius of 0.60 cm. A 200-N horizontal force is applied to the television set. How far does it move sideways due to the deformation of the rubber pads if the pads do not slide on the floor? The shear modulus of these rubber pads is 2.6 × 106 Pa. a. 6.8 mm b. 1.3 mm c. 1.7 mm d. 1.5 mm e. 3.4 mm

c. 1.7 mm

An athlete holds a 7.5-kg shot put in his hand with his lower arm horizontal, as shown in the figure. His lower arm has a mass of 2.8 kg and its center of gravity (or center of mass) is 12 cm from the elbow-joint pivot. How much force must the extensor muscle (which is M in the figure) in the upper arm exert on the lower arm? a. 100 N b. 500 N c. 1000 N d. 1500 N

c. 1000 N

Initially, a small 2.0-kg rock is whirling at the end of a very thin string in a circular path of radius 0.75 m on a horizontal frictionless surface, as shown in the figure. The initial tangential speed of the rock was 5.0 m/s. The string has been slowly winding around a vertical rod, and a few seconds later the length of the string has shortened to 0.25 m. What is the instantaneous speed of the mass at the moment the string reaches a length of 0.25 m? a. 3.9 m/s b. 9.3 m/s c. 15 m/s d. 225 m/s e. 75 m/s

c. 15 m/s

Two dogs, Rover and Fido, run on a level frictionless surface. Rover runs eastward with a momentum of 24 kg . m/s, and Fido runs northward with momentum 10 kg . m/s. They make a sudden perfectly inelastic collision. What is the magnitude of their combined momentum after the collision? It cannot be determined without knowing the masses and velocities of the dogs. a. 14 kg . m/s b. 34 kg . m/s c. 26 kg . m/s

c. 26 kg . m/s

If you want to double the momentum of a gas molecule, by what factor must you increase its kinetic energy? a. 16 b. 2 sqrt(2) c. 4 d. 2 e. sqrt(2)

c. 4

A 385-g tile hangs from one end of a string that goes over a pulley with a moment of inertia of 0.0125 kg *m^2 and a radius of 15.0 cm. A mass of 710 g hangs from the other end of the string. When the tiles are released, the larger one accelerates downward while the lighter one accelerates upward. The pulley has no friction in its axle and turns without the string slipping. What is the tension in the string on the side of the 710-g tile? a. 9.77 N b. 6.87 N c. 5.59 N d. 4.41 N e. 3.68 N

c. 5.59 N

Astronaut Jennifer's lifeline to her spaceship comes loose and she finds herself stranded, "floating" 100 m from the mothership. She suddenly throws her 2.00-kg wrench at 20 m/s in a direction away from the ship. If she and her spacesuit have a combined mass of 200 kg, how long does it take her to coast back to her spaceship? a. 1000 s b. 750 s c. 500 s d. 250 s e. 2.50 min

c. 500 s

A 1200-kg car is being raised at a constant speed if 25 cm/s by a crane, using a 20-m long steel cable that is 1.5 cm in diameter. Young's modulus for steel is 2.0 × 1011 Pa. What is the change in length of the cable caused by the car? a. 3.3 mm b. 3.3 m c. 6.7 mm d. 6.7 cm e. 3.3 cm

c. 6.7 mm

To drive a typical car at 40 mph on a level road for one hour requires about 3.2 × 107 J of energy. Suppose we tried to store this much energy in a spinning, solid, uniform, cylindrical flywheel. A large flywheel cannot be spun too fast or it will fracture. If we used a flywheel of diameter 1.2 m and mass 400 kg, what angular speed would be required to store 3.2 × 107 J? a. 1800 rad/s b. 3600 rad/s c. 940 rad/s d. 530 rad/s e. 5500 rad/s

c. 940 rad/s

To drive a typical car at 40 mph on a level road for one hour requires about 3.2 × 107 J of energy. Suppose we tried to store this much energy in a spinning, solid, uniform, cylindrical flywheel. A large flywheel cannot be spun too fast or it will fracture. If we used a flywheel of diameter 1.2 m and mass 400 kg, what angular speed would be required to store 3.2 × 107 J? a. 1800 rad/s b. 3600 rad/s c. 940 rad/s d. 530 rad/s e. 5500 rad/s

c. 940 rad/s

In a collision between two unequal masses, which mass receives a greater magnitude impulse? a. the larger mass b. the smaller mass c. They receive equal impulses.

c. They receive equal impulses.

A large 75-kg lighting fixture can be hung from wires of identical size and shape made of aluminum, brass, or copper. The values of Young's modulus for these metals are 0.70 × 1011 Pa (aluminum), 0.91 × 1011 (brass), and 1.1 × 1011 (copper). Which wire would stretch the least distance? a. aluminum b. brass c. copper d. They will all stretch the same distance.

c. copper

Which of the following quantities are units of momentum? (There could be more than one correct choice.) a. N*m b. kg*s/m c. kg*m/s d. N*s e. kg*m2/s2

c. kg*m/s d. N*s

A 25-kg piece of equipment can be hung by steel wires of length 1.00 m, 2.00 m, or 3.00 m. If all the wires have the same diameter, which one will stretch the greatest distance? a. the 1.00-m wire b. the 2.00-m wire c. the 3.00-m wire d. They will all stretch by the same distance.

c. the 3.00-m wire

Two objects of different mass have equal, non-zero kinetic energies. Which object has the greater magnitude momentum? a. They both have the same magnitude momentum. b. the lighter object c. the heavier object

c. the heavier object

As one stretches a metal wire, which condition is reached first? a. the elastic limit b. the breaking point c. the proportional limit

c. the proportional limit

When a car is weighed, it is driven slowly on a horizontal floor over a scale that records a reading as the front wheels go over the scale, and then records a second reading as the rear wheels go over the scale. The weight of the car is equal to a. the average of the two weights. b. the weight under the rear wheels. c. the sum of the two weights. d. the weight under the front wheels. e. the difference of the two weights.

c. the sum of the two weights.

A 5000-N force compresses a steel block by 0.0025 cm. How much force, applied over the same area, would be needed to compress the block by 0.0125 cm? a. 1,000 N b. 2,500 N c. 5,000 N d. 25,000 N

d. 25,000 N

A 25-kg piece of equipment can be hung by steel wires of length 1.00 m, 2.00 m, or 3.00 m. If all the wires have the same diameter, which one will stretch the greatest percent? a. the 1.00-m wire b. the 2.00-m wire c. the 3.00-m wire d. They will all stretch by the same percent.

d. They will all stretch by the same percent.

Tensile stress is a. the strain per unit length. b. the ratio of the change in length. c. the same as force. d. applied force per cross-e. sectional area.

d. applied force per cross-e. sectional area.

As shown in the figure, two blocks are connected by a light string that passes over a frictionless pulley having a moment of inertia of 0.0040 kg m2 and diameter 10 cm. The coefficient of kinetic friction between the table top and the upper block is 0.30. The blocks are released from rest, and the string does not slip on the pulley. How fast is the upper block moving when the lower one has fallen 0.60 m? a. 1.2 m/s b. 5.4 m/s c. 3.2 m/s d. 2.0 m/s e. 1.4 m/s

e. 1.4 m/s

A solid uniform cylinder is rolling without slipping. What fraction of its kinetic energy is rotational? a. 1/2 b. 3/4 c. 2/3 d. 1/4 e. 1/3

e. 1/3

A child is trying to stack two uniform bricks, each 24 cm long, so they will protrude as far as possible over the edge of a table without tipping over, as shown in the figure. What is the maximum possible overhang distance d? a. 10 cm b. 12 cm c. 14 cm d. 16 cm e. 18 cm

e. 18 cm

A man in a gym is holding an 8.0-kg weight at arm's length, a distance of 0.55 m from his shoulder joint. What is the torque about his shoulder joint due to the weight if his arm is held at 30° below the horizontal? a. 22 N m b. 2.2 N m c. 4.4 N m d. 13 N m e. 37 N m

e. 37 N m

A 5.00-m-long uniform ladder, weighing 200 N, rests against a smooth vertical wall with its base on a horizontal rough floor, a distance of 1.20 m away from the wall. The coefficient of static friction between the ladder and the floor is 0.200. How far up the ladder, measured along the ladder, can a 600-N person climb before the ladder begins to slip? a. 1.50 m b. 1.26 m c. 1.05 m d. 3.95 m e. 4.56 m

e. 4.56 m

If the answer to your calculation has units of kg m2/s2 , what type of quantity could it be? (There could be more than one correct choice.) a. angular momentum b. power c. linear momentum d. moment of inertia force e. work f. rotational kinetic energy g. torque

e. work f. rotational kinetic energy g. torque