Question 1

A 10 kg box rests on a horizontal floor. If the coefficient of static friction between the box and the floor is $$\mu_s = 0.4$$, what is the maximum force that can be applied horizontally before the box starts to move?

Accepted Answer

$$39.2\ \mathrm{N}$$

Question 2

Which statement best describes the direction of the frictional force acting on an object sliding across a surface?

Accepted Answer

It acts opposite to the direction of motion.

Question 3

A car of mass $$1200\ \mathrm{kg} is $$moving in a circle of radius $$30\ \mathrm{m} at a $$constant speed of $$15\ \mathrm{m/s}. $$What is the magnitude of the required centripetal force?

Accepted Answer

$$7200\ \mathrm{N}$$

Question 4

Which of the following best explains why the coefficient of friction is nearly independent of the area of contact between two surfaces?

Accepted Answer

Because the microscopic contact points do not change significantly with area.

Question 5

A spring with spring constant $$k = 250\ \mathrm{N/m} is $$compressed by $$0.2\ \mathrm{m}. $$What is the magnitude of the force exerted by the spring according to Hooke's Law?

Accepted Answer

$$50\ \mathrm{N}$$

Question 6

A block is pulled across a horizontal surface with a constant velocity. If the coefficient of kinetic friction is $$\mu_k = 0.2$$ and the normal force is $$100\ \mathrm{N}$$, what is the magnitude of the frictional force?

Accepted Answer

$$20\ \mathrm{N}$$

Question 7

Which of the following is true about static and kinetic friction?

Accepted Answer

The maximum static friction is generally greater than kinetic friction.

Question 8

A 5 kg object is attached to a spring and pulled so that the spring stretches by $$0.1\ \mathrm{m}. If $$the spring constant is $$k = 300\ \mathrm{N/m}$$, what is the restoring force exerted by the spring?

Accepted Answer

$$30\ \mathrm{N}$$

Question 9

A car is driving around a flat circular track of radius $$50\ \mathrm{m}. If $$the maximum static friction force between the tires and the road is $$4000\ \mathrm{N}$$, what is the maximum speed the car can have without skidding? (Assume $$m = 1000\ \mathrm{kg})$$

Accepted Answer

$$14.1\ \mathrm{m/s}$$

Question 10

Which of the following real-world scenarios best illustrates the concept of kinetic friction?

Accepted Answer

A sled sliding down a snowy hill.

Question 11

A block is at rest on an inclined plane. As the angle of the incline increases, which of the following best describes the behavior of the static friction force?

Accepted Answer

It increases as the angle increases, up to a maximum value.

Question 12

A 2 kg block is connected to a 3 kg block by a light string over a frictionless pulley. The 2 kg block rests on a horizontal surface with $$\mu_k = 0.1. $$What is the acceleration of the system when released? (Assume $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$3.92\ \mathrm{m/s^2$}$$

Question 13

Which equation correctly represents Hooke's Law for a spring?

Accepted Answer

$$F = -kx$$

Question 14

On a banked curve, which force helps a car to safely travel at higher speeds without skidding?

Accepted Answer

The component of the normal force parallel to the road surface.

Question 15

A 1.5 kg block is attached to a spring and oscillates back and forth. If the spring constant is $$k = 200\ \mathrm{N/m}$$ and the maximum displacement is $$0.05\ \mathrm{m}$$, what is the maximum force exerted by the spring?

Accepted Answer

$$10\ \mathrm{N}$$

Question 16

Which of the following would increase the maximum static friction force between a box and the floor?

Accepted Answer

Increasing the coefficient of static friction.

Question 17

A cyclist rounds a flat curve of radius $$20\ \mathrm{m} at a $$speed of $$10\ \mathrm{m/s}. If $$the coefficient of static friction between the tires and the road is $$0.5$$, what is the minimum normal force required to prevent slipping? (Assume $$m = 70\ \mathrm{kg}$$, $$g = 9.8\ \mathrm{m/s^2$})$$

Accepted Answer

$$686\ \mathrm{N}$$

Question 18

Which of the following is NOT a force that can provide the centripetal force for uniform circular motion?

Accepted Answer

Buoyant force

Applications of Newton's Laws: Friction, Springs, and Circular Motion

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