Force Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Force.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

A push or pull interaction between two objects that can cause a change in an object's velocity (speed or direction), described as a vector quantity.

Anything that makes something move, stop, speed up, slow down, or change direction.

Read the full concept explanation →

How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Force asks students to choose the object, list external interactions, and reason from the resulting force or torque pattern.

Common stuck point: Students often know a formula related to force but skip the recognition step: Have I isolated one system and listed the external forces or torques acting on it before applying a law? That leads to a correct-looking substitution attached to the wrong physical model.

Sense of Study hint: Ask: Have I isolated one system and listed the external forces or torques acting on it before applying a law?

Worked Examples

Example 1

easy

5 \text{ kg}

box is pushed across a floor with a force of

20 \text{ N}

. If there is no friction, what is the acceleration of the box?

No friction — the 20 N push is the only horizontal force, so a = F/m = 20/5 = 4 m/s².

Answer

a = 4 \text{ m/s}^2

First step

Identify the given values: mass

m = 5 \text{ kg}

, applied force

F = 20 \text{ N}

, and no friction.

Full solution

2
Apply Newton's second law: $F = ma$
3
Solve for acceleration: $a = \frac{F}{m} = \frac{20}{5} = 4 \text{ m/s}^2$

Force is a push or pull that causes a change in an object's motion. When a net force acts on an object, it accelerates according to Newton's second law

F = ma

Example 2

medium

Two forces act on an object:

F_1 = 15 \text{ N}

to the right and

F_2 = 8 \text{ N}

to the left. What is the net force on the object?

Net force = 15 − 8 = 7 N to the right.

Example 3

medium

7 \text{ kg}

sled is pushed forward with

40 \text{ N}

while friction pulls back with

12 \text{ N}

. Find the acceleration.

F_net = 40 − 12 = 28 N → a = 28/7 = 4 m/s².

Example 4

medium

0.5 \text{ kg}

ball changes velocity from

3 \text{ m/s}

east to

3 \text{ m/s}

west in

0.1 \text{ s}

after being hit by a bat. Find the average force from the bat.

Example 5

medium

Forces

8 \text{ N}

east,

6 \text{ N}

north, and

4 \text{ N}

west act on a

1 \text{ kg}

point. Find the magnitude of the net force.

Example 6

hard

1200 \text{ kg}

car traveling at

30 \text{ m/s}

brakes to rest over

60 \text{ m}

. Find the average braking force.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy

A force of

12 \text{ N}

acts on a

3 \text{ kg}

object. What acceleration does the object experience?

Example 2

medium

2.5 \text{ kg}

drone speeds up from

4 \text{ m/s}

10 \text{ m/s}

3 \text{ s}

while flying straight. What net force acts on the drone?

Drone accelerates at 2 m/s², so F_net = ma = 2.5 × 2 = 5 N.

Example 3

easy

A net force of

20\text{ N}

acts on a

4\text{ kg}

cart. Find its acceleration.

Example 4

easy

Is force a vector or a scalar quantity?

Example 5

easy

What is the net force on a

3\text{ kg}

block accelerating at

2\text{ m/s}^2

F = ma = 3 × 2 = 6 N.

Example 6

easy

Two forces,

7\text{ N}

right and

3\text{ N}

left, act on an object. Find the net force.

Net force = 7 − 3 = 4 N to the right.

Example 7

easy

Name the SI unit of force.

Example 8

easy

A book rests on a table at constant rest. What is the net force on it?

Equal and opposite forces → F_net = 0 N.

Example 9

easy

10\text{ N}

force pushes a

5\text{ kg}

box on a frictionless floor. Find the acceleration.

No friction → F_net = 10 N, a = 10/5 = 2 m/s².

Example 10

easy

Does a force always cause motion to start?

Example 11

medium

Three forces act on a point:

6\text{ N}

east,

6\text{ N}

west, and

8\text{ N}

north. Find the net force.

East and west cancel → F_net = 8 N north.

Example 12

medium

Forces

3\text{ N}

east and

4\text{ N}

north act on an object. Find the magnitude of the net force.

Pythagorean sum: √(3² + 4²) = 5 N.

Example 13

medium

2\text{ kg}

object goes from

0

6\text{ m/s}

3\text{ s}

. Find the net force.

Example 14

medium

5\text{ kg}

box has a

30\text{ N}

push forward and

10\text{ N}

friction back. Find the acceleration.

Net force = 30 − 10 = 20 N → a = 20/5 = 4 m/s².

Example 15

medium

An object moves at constant

10\text{ m/s}

. What net force acts on it?

Example 16

medium

A force gives a

4\text{ kg}

mass

3\text{ m/s}^2

. What acceleration does the same force give an

8\text{ kg}

mass?

Example 17

medium

Two ropes pull a ring:

5\text{ N}

north and

12\text{ N}

east. Find the resultant magnitude.

Resultant = √(5² + 12²) = √169 = 13 N.

Example 18

medium

Why does a resting object on a table experience zero net force despite gravity pulling it down?

N = W, so F_net = 0 N — the object stays at rest.

Example 19

challenge

2\text{ kg}

puck feels

6\text{ N}

east and

8\text{ N}

north simultaneously. Find its acceleration magnitude.

Resultant F = √(6² + 8²) = 10 N → a = 10/2 = 5 m/s².

Example 20

challenge

3\text{ kg}

block on a frictionless ramp has a gravity component of

15\text{ N}

along the slope. Find its acceleration along the ramp.

The 15 N slope component is the net force → a = 15/3 = 5 m/s² down the slope.

Example 21

challenge

4\text{ kg}

object at rest is pushed by

24\text{ N}

for

2\text{ s}

. How far does it travel?

Example 22

medium

6\text{ kg}

object feels a

30\text{ N}

net force north. Find its acceleration and direction.

F_net = 30 N north → a = 30/6 = 5 m/s² north.

Example 23

easy

A net force of

18 \text{ N}

acts on a

6 \text{ kg}

object. What is its acceleration?

Example 24

easy

9 \text{ kg}

object accelerates at

2 \text{ m/s}^2

. What net force acts on it?

Example 25

easy

A skydiver falls at constant terminal velocity. What is the net force on her?

Example 26

easy

2 \text{ kg}

ball is in free fall near Earth's surface. What is the net force on it? Use

g = 9.8 \text{ m/s}^2

In free fall, weight W = mg = 2 × 9.8 = 19.6 N is the only force.

Example 27

medium

1500 \text{ kg}

car accelerates from rest to

20 \text{ m/s}

8 \text{ s}

. What average net force acted on it?

Example 28

medium

Three coplanar forces act at a point:

10 \text{ N}

east,

10 \text{ N}

west, and

24 \text{ N}

south. Find the magnitude of the net force.

Example 29

medium

A force of

9 \text{ N}

east and a force of

12 \text{ N}

north act on a

1.5 \text{ kg}

block. Find the magnitude of its acceleration.

Example 30

medium

A horizontal force of

50 \text{ N}

accelerates a

10 \text{ kg}

box at

3 \text{ m/s}^2

on a rough floor. Find the friction force.

F_net = ma = 30 N; friction f = 50 − 30 = 20 N.

Example 31

medium

An object of unknown mass accelerates at

2 \text{ m/s}^2

under a

14 \text{ N}

net force. Find its mass.

Example 32

medium

0.2 \text{ kg}

apple sits in your hand at rest. What is the net force on the apple, and what upward force does your hand provide? Use

g = 9.8 \text{ m/s}^2

At rest: F_hand = W = mg = 0.2 × 9.8 = 1.96 N upward.

Example 33

hard

5 \text{ kg}

block accelerates from

2 \text{ m/s}

8 \text{ m/s}

over a distance of

15 \text{ m}

. Find the net force on it.

Example 34

hard

Two blocks of masses

3 \text{ kg}

and

5 \text{ kg}

are in contact on a frictionless surface. A horizontal force of

16 \text{ N}

pushes the

3 \text{ kg}

block. Find the contact force between the blocks.

Example 35

hard

2 \text{ kg}

block on a frictionless incline of

30^\circ

is held in place by a rope parallel to the slope. Find the tension in the rope. Use

g = 10 \text{ m/s}^2

T = mg sin 30° = 2 × 10 × 0.5 = 10 N.

Example 36

hard

An elevator of mass

400 \text{ kg}

accelerates upward at

2 \text{ m/s}^2

. Find the tension in the supporting cable. Use

g = 10 \text{ m/s}^2

T − W = ma → T = m(g + a) = 400 × 12 = 4800 N.

Example 37

hard

0.4 \text{ kg}

ball is whirled in a horizontal circle of radius

0.5 \text{ m}

5 \text{ m/s}

. Find the centripetal force.

Example 38

hard

A constant net force of

12 \text{ N}

acts on a

3 \text{ kg}

object initially at rest for

5 \text{ s}

. How far does it travel?

Example 39

hard

Two ropes pull a

5 \text{ kg}

ring:

30 \text{ N}

0^\circ

(east) and

40 \text{ N}

90^\circ

(north). Find the magnitude of the ring's acceleration.

Example 40

challenge

2 \text{ kg}

block is on a frictionless ramp inclined at

\theta

above horizontal. A horizontal push

P

holds it stationary. Express

P

in terms of

\theta

(

g = 10 \text{ m/s}^2

Example 41

challenge

Two masses,

3 \text{ kg}

and

5 \text{ kg}

, are connected by a light string over a frictionless pulley (Atwood machine). Find the acceleration and the string tension. Use

g = 10 \text{ m/s}^2

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Related Concepts

Acceleration Mass Newton's First Law Newton's Second Law Newton's Third Law

Background Knowledge

These ideas may be useful before you work through the harder examples.

accelerationmass