Question 1

A boy pulls a wooden box along a rough horizontal floor at constant speed by means of a force as shown. In the diagram f is the magnitude of the force of friction, N is the magnitude of the normal force, and Fg is the magnitude of the force of gravity. Which of the following must be true?

Accepted Answer

A)  P = f and N = Fg 
B)  P = f and N > Fg 
C)  P > f and N g  
D)  P > f and N = Fg  
E)  none of these

Question 2

The coefficient of kinetic friction:

Accepted Answer

A)  is in the direction of the frictional force 
B)  is in the direction of the normal force 
C)  is the ratio of force to area 
D)  can have units of newtons 
E)  none of the above

Question 3

A ball is thrown upward into the air with a speed that is greater than terminal speed. It lands at the place where it was thrown. During its flight the force of air resistance is the greatest:

Accepted Answer

A)  just after it is thrown 
B)  halfway up 
C)  at the top of its trajectory 
D)  halfway down 
E)  just before it lands

Question 4

The speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s2. The coefficient of kinetic friction between the puck and ice is:

Accepted Answer

A)  0.062 
B)  0.25 
C)  0.41 
D)  0.62 
E)  1.2

Question 5

A force (larger than the largest possible force of static friction) is applied to the left to an object moving to the right on a horizontal surface. Then:

Accepted Answer

A)  the object must be moving at constant speed 
B)  and the friction force act in opposite directions 
C)  the object must be slowing down 
D)  the object must be speeding up 
E)  the object will come to rest and remain at rest

Question 6

A horizontal shove of at least 200-N is required to start moving an 800-N crate initially at rest on a horizontal floor. The coefficient of static friction is:

Accepted Answer

A)  0.125 
B)  0.25 
C)  0.50 
D)  4.00 
E)  none of these

Question 7

A brick slides on a horizontal surface. Which of the following will increase the frictional force on it?

Accepted Answer

A)  Putting a second brick on top 
B)  Decreasing the surface area of contact 
C)  Increasing the surface area of contact 
D)  Decreasing the mass of the brick 
E)  None of the above

Question 8

A horizontal force of 5.0 N pushes a 0.50-kg block against a vertical wall. The block is initially at rest. If $\mu$s = 0.60 and $\mu$k = 0.50, the frictional force after a period of time is:

Accepted Answer

A)  0 N 
B)  2.5 N 
C)  3.0 N 
D)  4.0 N 
E)  4.9 N

Question 9

A crate resting on a rough horizontal floor is to be moved horizontally. The coefficient of static friction is 0.40. To start the crate moving with the weakest possible applied force, in what direction should the force be applied?

Accepted Answer

A)  Horizontal 
B)  24 $\degree$ below the horizontal 
C)  22 $\degree$ above the horizontal 
D)  24 $\degree$ above the horizontal 
E)  66 $\degree$ below the horizontal

Question 10

In uniform circular motion,

Accepted Answer

A)  the acceleration is always constant in magnitude and direction. 
B)  the velocity is always constant in magnitude and direction. 
C)  both the acceleration and the velocity are continually changing direction. 
D)  the velocity is always changing direction but the acceleration is always in the same direction. 
E)  the net force is always constant in magnitude and direction.

Question 11

One end of a 1.0-m long string is fixed; the other end is attached to a 2.0-kg stone. The stone swings in a vertical circle, passing the bottom point at 4.0 m/s. The tension force of the string at this point is about:

Accepted Answer

A)  0 N 
B)  12 N 
C)  20 N 
D)  32 N 
E)  52 N

Question 12

The same heavy wooden block is dragged by a force along a rough steel plate, as shown below for two possible situations. The magnitude of the acceleration is the same for the two situations; do not assume that the magnitude of is the same. The magnitude of the frictional force in (ii), as compared with that in (i) is:

Accepted Answer

A)  the same 
B)  greater 
C)  less 
D)  less for some angles and greater for others 
E)  can be less or greater, depending on the magnitude of the applied force.

Question 13

A car rounds a 75-m radius curve at a constant speed of 18 m/s. A ball is suspended by a string from the ceiling the car and moves with the car. The angle between the string and the vertical is:

Accepted Answer

A)  0° 
B)  1.4° 
C)  24° 
D)  90° 
E)  cannot be found without knowing the mass of the ball

Question 14

An object of mass m and another object of mass 2m are each forced to move along a circle of radius 1.0 m at a constant speed of 1.0 m/s. The magnitudes of their accelerations are:

Accepted Answer

A)  equal 
B)  in the ratio of : 1 
C)  in the ratio of 2 : 1 
D)  in the ratio of 4 : 1 
E)  zero

Question 15

The system shown remains at rest. The force of friction on the block on the slope is:

Accepted Answer

A)  4 N 
B)  8 N 
C)  12 N 
D)  16 N 
E)  20 N

Question 16

An automobile moves on a level horizontal road in a circle of radius 30 m. The coefficient of friction between tires and road is 0.50. The maximum speed with which this car can round this curve is:

Accepted Answer

A)  3.0 m/s 
B)  4.9 m/s 
C)  9.8 m/s 
D)  12 m/s 
E)  147 m/s

Question 17

A 5.0-kg crate is on an incline that makes an angle of 30$\degree$with the horizontal. If the coefficient of static friction is 0.50, the minimum force that can be applied parallel to the plane to hold the crate at rest is:

Accepted Answer

A)  0 N 
B)  3.3 N 
C)  21 N 
D)  25 N 
E)  46 N

Question 18

Block A, with a mass of 10 kg, rests on a 30$\degree$incline. The coefficient of kinetic friction is 0.20. The attached string is parallel to the incline and passes over a massless, frictionless pulley at the top. Block B, with a mass of 8.0 kg, is attached to the dangling end of the string. The acceleration of B is:

Accepted Answer

A)  0.69 m/s2, up 
B)  0.69 m/s2, down 
C)  2.6 m/s2, up 
D)  2.6 m/s2, down 
E)  0 m/s2

Question 19

In uniform circular motion,

Accepted Answer

A)  the acceleration always points away from the center of the circle. 
B)  the velocity always points towards the center of the circle. 
C)  the acceleration and the velocity are always parallel. 
D)  the acceleration and the velocity are always perpendicular. 
E)  there is no fixed relationship between the direction of the acceleration and the direction of the velocity.

Question 20

A crate rests on a horizontal surface and a woman pulls on it with a 10-N force. No matter what the orientation of the force, the crate does not move. Rank the situations shown below according to the magnitude of the frictional force of the surface on the crate, least to greatest.

Accepted Answer

A)  1, 2, 3 
B)  2, 1, 3 
C)  2, 3, 1 
D)  1, 3, 2 
E)  3, 2, 1

Exam 6: Force and Motion II

A boy pulls a wooden box along a rough horizontal floor at constant speed by means of a force as shown. In the diagram f is the magnitude of the force of friction, N is the magnitude of the normal force, and F_gis the magnitude of the force of gravity. Which of the following must be true?

The coefficient of kinetic friction:

A ball is thrown upward into the air with a speed that is greater than terminal speed. It lands at the place where it was thrown. During its flight the force of air resistance is the greatest:

The speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s². The coefficient of kinetic friction between the puck and ice is:

A force (larger than the largest possible force of static friction) is applied to the left to an object moving to the right on a horizontal surface. Then:

A horizontal shove of at least 200-N is required to start moving an 800-N crate initially at rest on a horizontal floor. The coefficient of static friction is:

A brick slides on a horizontal surface. Which of the following will increase the frictional force on it?

A horizontal force of 5.0 N pushes a 0.50-kg block against a vertical wall. The block is initially at rest. If $\mu$ _s = 0.60 and $\mu$ _k = 0.50, the frictional force after a period of time is:

A crate resting on a rough horizontal floor is to be moved horizontally. The coefficient of static friction is 0.40. To start the crate moving with the weakest possible applied force, in what direction should the force be applied?

In uniform circular motion,

One end of a 1.0-m long string is fixed; the other end is attached to a 2.0-kg stone. The stone swings in a vertical circle, passing the bottom point at 4.0 m/s. The tension force of the string at this point is about:

A car rounds a 75-m radius curve at a constant speed of 18 m/s. A ball is suspended by a string from the ceiling the car and moves with the car. The angle between the string and the vertical is:

An object of mass m and another object of mass 2m are each forced to move along a circle of radius 1.0 m at a constant speed of 1.0 m/s. The magnitudes of their accelerations are:

The system shown remains at rest. The force of friction on the block on the slope is:

An automobile moves on a level horizontal road in a circle of radius 30 m. The coefficient of friction between tires and road is 0.50. The maximum speed with which this car can round this curve is:

A 5.0-kg crate is on an incline that makes an angle of 30 $\degree$ with the horizontal. If the coefficient of static friction is 0.50, the minimum force that can be applied parallel to the plane to hold the crate at rest is:

In uniform circular motion,

A crate rests on a horizontal surface and a woman pulls on it with a 10-N force. No matter what the orientation of the force, the crate does not move. Rank the situations shown below according to the magnitude of the frictional force of the surface on the crate, least to greatest.

Exam 6: Force and Motion II

A boy pulls a wooden box along a rough horizontal floor at constant speed by means of a force as shown. In the diagram f is the magnitude of the force of friction, N is the magnitude of the normal force, and Fg is the magnitude of the force of gravity. Which of the following must be true?

The coefficient of kinetic friction:

A ball is thrown upward into the air with a speed that is greater than terminal speed. It lands at the place where it was thrown. During its flight the force of air resistance is the greatest:

The speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s2. The coefficient of kinetic friction between the puck and ice is:

A force (larger than the largest possible force of static friction) is applied to the left to an object moving to the right on a horizontal surface. Then:

A horizontal shove of at least 200-N is required to start moving an 800-N crate initially at rest on a horizontal floor. The coefficient of static friction is:

A brick slides on a horizontal surface. Which of the following will increase the frictional force on it?

A horizontal force of 5.0 N pushes a 0.50-kg block against a vertical wall. The block is initially at rest. If μ\muμ s = 0.60 and μ\muμ k = 0.50, the frictional force after a period of time is:

A crate resting on a rough horizontal floor is to be moved horizontally. The coefficient of static friction is 0.40. To start the crate moving with the weakest possible applied force, in what direction should the force be applied?

In uniform circular motion,

One end of a 1.0-m long string is fixed; the other end is attached to a 2.0-kg stone. The stone swings in a vertical circle, passing the bottom point at 4.0 m/s. The tension force of the string at this point is about:

A car rounds a 75-m radius curve at a constant speed of 18 m/s. A ball is suspended by a string from the ceiling the car and moves with the car. The angle between the string and the vertical is:

An object of mass m and another object of mass 2m are each forced to move along a circle of radius 1.0 m at a constant speed of 1.0 m/s. The magnitudes of their accelerations are:

The system shown remains at rest. The force of friction on the block on the slope is:

An automobile moves on a level horizontal road in a circle of radius 30 m. The coefficient of friction between tires and road is 0.50. The maximum speed with which this car can round this curve is:

A 5.0-kg crate is on an incline that makes an angle of 30 °\degree° with the horizontal. If the coefficient of static friction is 0.50, the minimum force that can be applied parallel to the plane to hold the crate at rest is:

In uniform circular motion,

A crate rests on a horizontal surface and a woman pulls on it with a 10-N force. No matter what the orientation of the force, the crate does not move. Rank the situations shown below according to the magnitude of the frictional force of the surface on the crate, least to greatest.

A boy pulls a wooden box along a rough horizontal floor at constant speed by means of a force as shown. In the diagram f is the magnitude of the force of friction, N is the magnitude of the normal force, and F_gis the magnitude of the force of gravity. Which of the following must be true?

The speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s². The coefficient of kinetic friction between the puck and ice is:

A horizontal force of 5.0 N pushes a 0.50-kg block against a vertical wall. The block is initially at rest. If $\mu$ _s = 0.60 and $\mu$ _k = 0.50, the frictional force after a period of time is:

A 5.0-kg crate is on an incline that makes an angle of 30 $\degree$ with the horizontal. If the coefficient of static friction is 0.50, the minimum force that can be applied parallel to the plane to hold the crate at rest is: