FE Exam PROBLEMS - DYNAMICS
(Friction/Laws Of)

Problem 1

Which one of the following is incorrect?

a)  Frictional forces act to oppose motion.
b)  Frictional forces are parallel to surfaces.
c)  Frictional forces are dependent on contact area.
d)  Static friction is greater than kinetic friction.

Problem 2

Which one of the following is true?

a)  The coefficient of friction is a function of the normal force.
b)  The coefficient of friction is a function of material surfaces.
c)  The coefficient of friction can be greater than 1.
d)  Selections a) and b).

Problem 3

Considering the forces acting on the block shown in the figure below. If the pulling force (P) equals the friction force (Ffriction), which of the following is true?

a)  The block will remain stationary if the friction force is static.
b)  The block will accelerate if the friction force is kinetic.
c)  The block will move at constant velocity if the friction force is static.
d)  The block will begin to move if the friction force is static.

Problem 4

A block weighing W, is at rest on an incline as shown in the figure below. What is the static friction force F, acting on the block? (Note: m is the coefficient of friction)

a)  F =   Wcosa
b)  F =  -Wtana
c)  F =  -Wsina
d)  F =   N - W

Problem 5

A block weighing W = 10 N is being pushed by force P = 5 N as shown in the figure below.  If the block is stationary and motion is impending, what is the angle of friction?

a)  30.00 deg
b)  26.56 deg
c)  63.43 deg
d)  60.00 deg

Problem 6

A 3,000 lb car is moving (coasting) in a straight line on a horizontal road at 15 mph. If the coefficient of rolling friction between the cars tires and road is 0.04, how far will the car travel before it comes to a stop?

a)  143 ft
b)  213 ft
c)    96 ft
d)  188 ft

Problem 7

What is the rolling friction force of a 1500 kg car moving at constant velocity on a horizontal road? The coefficient of rolling friction is 0.04.

a)  248 N
b)  437 N
c)  588 N
d)  124 N

Problem 8

A 20 kg rectangular block having dimensions 100 cm x 50 cm x 75 cm rests on a horizontal surface.  If it takes a force of 5 N (applied horizontally) to get the block to move when it is resting on the side with dimensions 100 cm x 50 cm, how much force is required to get the block to move when it is resting on the side with dimensions 50cm x 75 cm?

a)     5.00 N
b)     6.67 N
c)     3.75 N
d)  10.00 N

Problem 9

A 20 kg block rests on a horizontal surface. If it takes a 5 N force (applied horizontally) to get the block to initially move, what is the kinetic friction force if the 5 N force is continually applied and held constant, given uk = 75% of us. (Note: uk is coefficient of kinetic friction,  us is coefficient of static friction)

a)  5 .00 N
b)  3.75 N
c)  6.25 N
d)  4.00 N

Problem 10

A 100 N block rests on a horizontal surface. If it takes a 10 N force (applied horizontally) to get the block to move, what force is required to get the block to move if another 100 N block is placed on top of it?

a)  20 N
b)    5 N
c)  40 N
d)  15 N