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Solved problems for the chapter:

Force

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Introduction to Force

1. What is force?

2. How do we know that a force is acting on a body?

2.1. Effects of forces

3. Name, symbol and unit of force

4. Properties of force

5. Drawing forces

6. Contact force or field force

7. Surface and volume distributed forces

7.1. Area-distributed or surface forces

7.2. Volume-distributed or body forces

8. Measuring forces

9. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:force/5061/

Example 1.

The table below describes events in which a force acts on one of the bodies described. Answer the questions on the columns for each event.

Event	On which body does the force act?	What do we call that force?	How do we know that a force acts on the body?
A car starts at a green light on a traffic light.
A brick breaks when it falls to the ground.
A child shapes a plasticine doll.
A snow avalanche starts on the hill and rushes into the valley with increasing speed.
A magnet attracts a needle on the ground.
We hold a spring in our hands and stretch it.
A child rotates on the hanging carousel seat.
We fill a balloon with air from the lungs.

Example 2.

Complete the table below with the appropriate values.

Subject	m	m	m	W
Traveller			20
Eraser	15
Student				520
Apple		17
Car			1350
Textbook				3.7

John pushes a cart with a force of 80 N, as shown in the picture below. How do we graphically represent this force?

Which of the following statements is/are correct?:

Force is known by its effect on a body.
The force unit, newton (N), is a fundamental unit of measurement.
We must always put an arrow above the force symbol.
The effect of the force on the body does not depend on the line of action.
The body can act with force on another body only by touch.
Force always acts at one point.

A wooden box weighing 40 dag lies on a flat surface. Draw to scale all the forces acting on the box.

For the force in the following examples, write how it is distributed: point, planar or spatial.

Using the tip of a pencil, push an eraser across a table. What is the force of the pencil on the eraser?
The wind blows against the sail and pushes a sailboat. What is the force of the wind on the sail?
A string on which the weight is hung is attached to the ceiling. What is the force of the string on the ceiling?
Magnet attracts pieces of iron. What is the magnet's force on iron?
A crate lies on the ground. What is the force of the crate on the ground?
An apple falls from a tree. What is the force acting on the apple while falling?

Determine whether contact or field force acts in the cases described.

A locomotive pulls a wagon.
Engine force is transmitted to the wheels of a car.
A skier descended a gorge.
Our hair gets tangled during a storm.
The wind pushes a sailboat.
Magnet attracts iron.
A brick acts with force on the ground.

Let's take an iron block and bring a horseshoe magnet closer to it, as shown in the picture. The magnet acts on a square side with a force of 20 N.

Name the force.
Determine its direction and line of action.
Draw the force with a selected scale.

A man walks on a tightrope and his weight is 500 N.

Draw his weight in a selected scale.
Where is the force with which his foot acts on the rope? What is this force?

10.

Force in the described phenomena causes deformation of the body - that is, a change in shape. From the description, determine whether the deformation was flexible.

Jane stretches the spring.
At tension, the elastic is torn.
Due to the weight of the snow, the branches bend.
Ice broke the trees.
Housewife kneads bread dough.
The wind bends the spruce.

11.

Which properties of an object can be changed by a force?

direction of motion, mass and speed
mass, shape and speed
direction of motion, shape and speed
direction of motion and speed only

12.

Which is an example of a force?

energy
power
pressure
weight

13.

Which properties of a body can be changed by applying a force to the body?

mass, motion and shape
mass and motion, but not shape
mass and shape, but not motion
motion and shape, but not mass