Question 1

A car experiences both a centripetal and a tangential acceleration. For which of the following would this be true?

Accepted Answer

A)  It is going around a curve at a constant speed. 
B)  It is going around a curve and slowing down. 
C)  It is going along a straight road at a constant speed. 
D)  It is going along a straight road and increasing its speed. 
E)  It is going along a straight road and decreasing its speed.

Question 2

A mass M = 5.6 kg on a horizontal table is pulled by a horizontal string that passes over a frictionless pulley to a free-hanging mass m = 3.4 kg. The coefficient of friction between M and the table is 0.28. The acceleration of M is

Accepted Answer

A)  3.7 m/s2.  
B)  2.0 m/s2.  
C)  2.2 m/s2.  
D)  0.20 m/s2.  
E)  0.49 m/s2.

Question 3

A mass m2 = 1.5 kg rests on a horizontal table. The coefficients of friction between m2 and the table are µs = 0.3 and µk = 0.25. The mass m2 is attached by strings to masses m1 = 2.5 kg and m3 = 4.5 kg as shown. Masses m1 and m3 hang freely. The system is initially held at rest. After it is released, the acceleration of m2 is approximately

Accepted Answer

A)  1.9 m/s2. 
B)  2.4 m/s2. 
C)  3.0 m/s2. 
D)  zero. 
E)  13 m/s2.

Question 4

A box m = 20 kg) is sitting on a horizontal surface. It is connected to a massless hook by a light string passing over a massless pulley wheel. The coefficients of friction between the box and the surface are 0.50 static) and 0.30 kinetic). On top of m is a second box M of mass 20 kg. The coefficients of friction between the boxes m and M are 0.80 static) and 0.60 kinetic). How much weight needs to be added to the hook until the box just begins to move?

Accepted Answer

A)  10 kg 
B)  98 kg 
C)  20 kg 
D)  16 kg 
E)  200 kg

Question 5

In drag racing, the driver deploys a parachute at the end of the mile run. The parachute works well because

Accepted Answer

A)  the dragster does not have any brakes to reduce weight. 
B)  the drag force due to the parachute is large at high speeds. 
C)  there is no rolling friction at high speeds. 
D)  the driver has no time to apply the brakes. 
E)  the deployment of the parachute is part of the show.

Question 6

An object with a mass of 5.5 kg is allowed to slide from rest down an inclined plane. The plane makes an angle of 30 o  with the horizontal and is 72 m long. The coefficient of friction between the plane and the object is 0.35. The speed of the object at the bottom of the plane is

Accepted Answer

A)  5.3 m/s. 
B)  15 m/s. 
C)  24 m/s. 
D)  17 m/s. 
E)  11 m/s.

Question 7

A block of mass mb rests on a horizontal surface and is accelerated by means of a horizontal cord that passes over a frictionless peg to a hanging weight of mass mw. The coefficient of kinetic friction between the block and the horizontal surface is µ and the tension in the cord is T. The acceleration of the block is given by

Accepted Answer

A)  T - mwg)/mw + mb). 
B)  T/µmbg + mb). 
C)  T - µmb)/mb. 
D)  mwg - T)/mw. 
E)  T/mb - µmbg.

Question 8

A tired worker pushes a heavy 100-kg) crate that is resting on a thick pile carpet. The coefficients of static and kinetic friction are 0.6 and 0.4, respectively. The worker pushes with a horizontal force of 490 N. The frictional force exerted by the surface is

Accepted Answer

A)  980 N. 
B)  588 N. 
C)  490 N. 
D)  392 N. 
E)  100 N.

Question 9

A block of mass m is at rest on an inclined plane that makes an angle of 30 o with the horizontal. Which of the following statements about the force of static friction is true?

Accepted Answer

A)  fs > mg 
B)  fs > mg cos 30o 
C)  fs = mg cos 30o 
D)  fs = mg sin 30o 
E)  None of these statements is true.

Question 10

A 2.0 kg-book is on the floor of an elevator. If the elevator is accelerating downward at a rate of , the normal force acting on the book by the floor is

Accepted Answer

A)  0 N. 
B)  2.0 N. 
C)  10 N. 
D)  20 N. 
E)  30 N.

Question 11

A 6000-kg truck is accelerating at 0.5 m/s2 up a slope of 5 degrees. If the opposing forces due to road friction and air resistance are 80 N per 1000 kg of truck mass, calculate the driving force needed for the truck to accelerate up the incline.

Accepted Answer

A)  8100 N 
B)  8600 N 
C)  8200 N 
D)  7700 N 
E)  1700 N

Question 12

In the equation F = bv, F is the force on an object that is moving in a viscous medium, b is a constant, and v is the speed of the falling object. The SI units of the constant b are

Accepted Answer

A)  m/s. 
B)  kg · s. 
C)  kg/s. 
D)  kg · m. 
E)  m/s2.

Question 13

An atomic force microscope consists of a cantilever with a very fine tip on one end. The lever is driven by a piezoelectric motor allowing the tip to scan a surface on an atomic scale. As it scans the surface, what is the main frictional force between the tip and the surface?

Accepted Answer

A)  static 
B)  kinetic 
C)  rolling 
D)  all three 
E)  There is no frictional force.

Question 14

A 2.0 kg-book is at rest on the horizontal floor. You are applying a 10 N downward force, on the book, at an angle of 60 o from the horizontal. The normal force on the book exerted by the floor is

Accepted Answer

A)  5.0 N. 
B)  10 N. 
C)  25 N. 
D)  28 N. 
E)  30 N.

Question 15

A block is placed on a plane whose angle of inclination is 30 o . The coefficients of static and kinetic friction for the block on the inclined plane are 0.7 and 0.5, respectively. The block

Accepted Answer

A)  remains stationary on the inclined plane. 
B)  accelerates down the inclined plane. 
C)  travels down the inclined plane at constant velocity. 
D)  travels up the inclined plane at constant velocity. 
E)  accelerates up the inclined plane.

Question 16

The system in the figure is moving with constant speed v to the right on a stationary ramp. The system will accelerate to the right if

Accepted Answer

A)  angle $\beta$ is increased. 
B)  angle $\alpha$ is increased. 
C)  coefficient of friction µk for surface A is increased. 
D)  coefficient of friction µk for surface B is increased. 
E)  normal force on block 2 is increased.

Question 17

An object with a mass M = 250 g is at rest on a plane that makes an angle $\theta$ = 30 o  above the horizontal. The coefficient of kinetic friction between M and the plane is µk = 0.100. Mass M is attached by a string to another mass, m = 200 g, which hangs freely. When mass m has fallen 30.0 cm, its speed is

Accepted Answer

A)  83 cm/s. 
B)  48 cm/s. 
C)  160 cm/s. 
D)  59 cm/s. 
E)  72 cm/s.

Question 18

A 2.0 kg-book is at rest on the horizontal floor. You are applying a 10 N downward force, on the book, at an angle of 30 o from the vertical. The normal force on the book exerted by the floor is

Accepted Answer

A)  5.0 N. 
B)  10 N. 
C)  25 N. 
D)  28 N. 
E)  30 N.

Question 19

A particle is moving uniformly in a circle with radius 50 cm. The linear speed of the particle is 60 cm/s. The acceleration of the particle has a magnitude of

Accepted Answer

A)  zero. 
B)  36 m/s2.  
C)  1.8 *0 105 cm/s2.  
D)  72 cm/s2.  
E)  3.6 m/s2.

Question 20

A block of mass m is pulled in the direction shown in the figure across a rough surface at a constant velocity. The magnitude of the frictional force is

Accepted Answer

A)  µkmg. 
B)  T cos $\theta$ 
C)  T - µkmg). 
D)  µkT sin $\theta$ 
E)  µkmg - T sin $\theta$).

Exam 5: Forces and Motion II: Applications

A car experiences both a centripetal and a tangential acceleration. For which of the following would this be true?

A mass M = 5.6 kg on a horizontal table is pulled by a horizontal string that passes over a frictionless pulley to a free-hanging mass m = 3.4 kg. The coefficient of friction between M and the table is 0.28. The acceleration of M is

In drag racing, the driver deploys a parachute at the end of the mile run. The parachute works well because

An object with a mass of 5.5 kg is allowed to slide from rest down an inclined plane. The plane makes an angle of 30^o with the horizontal and is 72 m long. The coefficient of friction between the plane and the object is 0.35. The speed of the object at the bottom of the plane is

A tired worker pushes a heavy 100-kg) crate that is resting on a thick pile carpet. The coefficients of static and kinetic friction are 0.6 and 0.4, respectively. The worker pushes with a horizontal force of 490 N. The frictional force exerted by the surface is

A block of mass m is at rest on an inclined plane that makes an angle of 30^owith the horizontal. Which of the following statements about the force of static friction is true?

A 2.0 kg-book is on the floor of an elevator. If the elevator is accelerating downward at a rate of , the normal force acting on the book by the floor is

A 6000-kg truck is accelerating at 0.5 m/s² up a slope of 5 degrees. If the opposing forces due to road friction and air resistance are 80 N per 1000 kg of truck mass, calculate the driving force needed for the truck to accelerate up the incline.

In the equation F = bv, F is the force on an object that is moving in a viscous medium, b is a constant, and v is the speed of the falling object. The SI units of the constant b are

An atomic force microscope consists of a cantilever with a very fine tip on one end. The lever is driven by a piezoelectric motor allowing the tip to scan a surface on an atomic scale. As it scans the surface, what is the main frictional force between the tip and the surface?

A 2.0 kg-book is at rest on the horizontal floor. You are applying a 10 N downward force, on the book, at an angle of 60^o from the horizontal. The normal force on the book exerted by the floor is

A block is placed on a plane whose angle of inclination is 30^o. The coefficients of static and kinetic friction for the block on the inclined plane are 0.7 and 0.5, respectively. The block

A 2.0 kg-book is at rest on the horizontal floor. You are applying a 10 N downward force, on the book, at an angle of 30^o from the vertical. The normal force on the book exerted by the floor is

A particle is moving uniformly in a circle with radius 50 cm. The linear speed of the particle is 60 cm/s. The acceleration of the particle has a magnitude of