Q: A spring scale is calibrated using a known mass of $$1.50\ \text{kg} on $$Earth. What force does the scale read?

$$F = m g = 1.50 \times 9.8 = 14.7\ \text{N}$$

Question 1

A crate weighing 500 N is pulled horizontally with a force of 230 N, but it does not move. What is the magnitude of the static friction force acting on the crate?

Accepted Answer

$$230\ 	ext{N}$$

Question 2

A spring with a spring constant $$k = 120\ 	ext{N/m} is $$stretched by $$\Delta L = 0.10\ 	ext{m}. $$What is the magnitude of the force exerted by the spring?

Accepted Answer

$$12\ 	ext{N}$$

Question 3

A toboggan slides down a hill inclined at angle $$\alpha$$ with constant speed. Which equation correctly relates the kinetic friction force $$f_k to $$the weight $$w$$ and the angle $$\alpha$$?

Accepted Answer

$$f_k = w \sin \alpha$$

Question 4

A car accelerates to the left, and a low-tech accelerometer inside shows a mass hanging at an angle $$\beta$$ from the vertical. Which force diagram best represents the forces acting on the mass?

Accepted Answer

Tension acts along the string, weight acts downward, and the net force is horizontal to the left.

Question 5

A block is pulled at an angle $$	heta$$ above the horizontal. Which equation gives the normal force $$n on $$the block?

Accepted Answer

$$n = w - T \sin 	heta$$

Question 6

A block slides across a rough surface. Which statement about friction is correct?

Accepted Answer

Kinetic friction is constant and depends only on the normal force and the coefficient of kinetic friction.

Question 7

A spring scale is calibrated using a known mass of $$1.50\ 	ext{kg} on $$Earth. What force does the scale read?

Accepted Answer

$$F = m g = 1.50 	imes 9.8 = 14.7\ 	ext{N}$$

Question 8

Which of the following is NOT a necessary condition for equilibrium of a particle?

Accepted Answer

The particle must be at rest.

Question 9

A block is placed on a horizontal surface. Which equation correctly gives the maximum static friction force?

Accepted Answer

$$f_{s,	ext{max}} = \mu_s n$$

Question 10

A block is pulled with a force $$F$$ and moves at constant speed. Which statement is true?

Accepted Answer

The pulling force equals the kinetic friction force.

Question 11

A block is attached to a spring and stretched. According to Hooke's Law, what is the direction of the spring force?

Accepted Answer

Opposite to the direction of displacement from equilibrium.

Question 12

A block is falling through a fluid and reaches terminal velocity. Which equation describes the equilibrium of forces?

Accepted Answer

$$D v^2$ = m g$$

Question 13

Which statement about the microscopic view of friction is correct?

Accepted Answer

Even smooth surfaces are rough at the microscopic level and tend to catch and cling.

Question 14

A block is pulled at an angle $$30^\circ$$ above the horizontal with a force $$T. $$Which equation gives the horizontal component of the pulling force?

Accepted Answer

$$T \cos 30^\circ$$

Question 15

A block is sliding down an inclined plane with angle $$\alpha. $$Which equation gives the component of weight parallel to the incline?

Accepted Answer

$$w \sin \alpha$$

Question 16

Which of the following is a real-world example of Newton's second law in action?

Accepted Answer

A car accelerating when the driver presses the gas pedal.

Question 17

A block is pulled horizontally with a force $$F$$ and moves at constant speed. If the coefficient of kinetic friction is $$\mu_k$$ and the weight is $$w$$, what is the value of $$F$$?

Accepted Answer

$$F = \mu_k w$$

Question 18

Which of the following is NOT a fundamental force in nature?

Accepted Answer

Frictional force

Question 19

A block is pulled horizontally with a force $$F$$ and moves at constant speed. If the mass of the block is $$m$$ and the coefficient of kinetic friction is $$\mu_k$$, what is the acceleration of the block?

Accepted Answer

$$0$$

Applications of Newton's Laws: Equilibrium, Friction, and Elastic Forces

Study Guide - Practice Questions

Study Guide - Flashcards