Question 1

A 10 kg box rests on a horizontal floor. The coefficient of static friction between the box and the floor is 0.5. What is the maximum horizontal force that can be applied to the box before it starts to move? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$49\ \mathrm{N}$$

Question 2

A skier is being towed up a frictionless slope at constant speed. Which of the following statements is correct about the net force acting on the skier?

Accepted Answer

The net force is zero because the skier moves at constant speed.

Question 3

A rock is sliding across the ground after being kicked. Which forces are acting on the rock at this moment?

Accepted Answer

Weight, normal force, and kinetic friction.

Question 4

A 70 kg skydiver falls at terminal speed with arms and legs spread. If the drag force equals the weight at terminal speed, what is the magnitude of the drag force? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$686\ \mathrm{N}$$

Question 5

Which of the following best describes the direction of the friction force acting on a box being pushed to the right across a rough surface?

Accepted Answer

To the left, opposing the motion.

Question 6

A 5 kg object is sliding on a horizontal surface with a coefficient of kinetic friction $$\mu_k = 0.2. $$What is the magnitude of the kinetic friction force acting on the object? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$9.8\ \mathrm{N}$$

Question 7

A hammer strikes a nail, driving it into a piece of wood. According to Newton's Third Law, which statement is correct?

Accepted Answer

The nail exerts a force on the hammer equal in magnitude and opposite in direction to the force the hammer exerts on the nail.

Question 8

A 2 kg object is dropped from rest in air. As it falls, the drag force increases until it equals the object's weight. What happens to the object's acceleration at this point?

Accepted Answer

The acceleration becomes zero and the object falls at constant speed.

Question 9

Which of the following factors does NOT affect the magnitude of the drag force on a falling object?

Accepted Answer

The object's mass.

Question 10

A person pushes a 20 kg box across a floor with a force of $$60\ \mathrm{N} to $$the right. The coefficient of kinetic friction is $$0.3. $$What is the acceleration of the box? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$0.18\ \mathrm{m/s^2$}$$

Question 11

A car tire pushes backward on the road. According to Newton's Third Law, what is the reaction force?

Accepted Answer

The road pushes forward on the tire.

Question 12

A 50 kg crate is at rest on a horizontal surface. The coefficient of static friction is $$0.4. $$What is the minimum force required to start moving the crate? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$196\ \mathrm{N}$$

Question 13

Which of the following statements about static and kinetic friction is correct?

Accepted Answer

Static friction can be greater than kinetic friction for the same two surfaces.

Question 14

A ball is dropped from a tall building. As it falls, which of the following best describes the forces acting on it before reaching terminal speed?

Accepted Answer

Weight acts downward and drag acts upward, but weight is greater than drag.

Question 15

A man pulls on a spring with a force of $$30\ \mathrm{N}. $$According to Newton's Third Law, what is the force exerted by the spring on the man?

Accepted Answer

$$30\ \mathrm{N} in $$the opposite direction.

Question 16

A 60 kg parachutist jumps from a plane and eventually reaches terminal speed. If the drag force is suddenly reduced (e.g., by folding arms), what happens to the parachutist's motion?

Accepted Answer

The parachutist accelerates downward until a new, higher terminal speed is reached.

Question 17

Which of the following is NOT a step in constructing a free-body diagram?

Accepted Answer

Drawing the object's trajectory over time.

Question 18

A 10 kg block is pulled across a horizontal surface with a force of $$60\ \mathrm{N}. $$The coefficient of kinetic friction is $$0.4. $$What is the net force acting on the block? (Take $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$20.8\ \mathrm{N}$$

Question 19

A peregrine falcon and a large rock have the same shape and cross-sectional area but different masses. Which one will have a higher terminal speed when falling through air?

Accepted Answer

The large rock, because it has greater mass.

Question 20

Which of the following best explains why you cannot walk on ice as easily as on concrete?

Accepted Answer

The coefficient of static friction between your shoes and ice is much lower than with concrete.

Friction, Forces, and Newton's Laws: Study Notes

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