Force, Work and Power

Question 0

What is force measured in?

Answer 0

Newtons (N)

Question 1

What is a force?

Answer 1

A force is any thing which can change the velocity of an object or make it move.

Question 2

Finish the sentence.

For every force…

Answer 2

an equal but opposite force is exerted

Question 3

What is friction?

Answer 3

Friction is a force which prevents the easy movement between two objects in contact.

Question 4

What can force be measured using?

Answer 4

a spring balance

Question 5

What is a law to do with force?

What does it state?

Answer 5

Hooke’s Law states that the extension of a spring depends on the force pulling on it (e.g. the weight of a mass attached to the spring).

Question 6

What is work?

Answer 6

Work is done when a force moves an object.

Question 7

What is work measured in?

Answer 7

Joules

Question 8

State the equation used to find work

Answer 8

Work(J) = Force(N) X Distance(M)

Question 9

What is power?

Answer 9

The rate at which work is done

Question 10

What is power measured in?

Answer 10

watts

Question 11

what is one watt in joules?

Answer 11

1 joule per second

Question 12

write in words a formula for the average power.

Answer 12

The average power (watts) is the work done (joules) divided by the time taken (seconds).

Question 13

Write out a formula for power

Answer 13

Power = Work done
—————
Time taken

Question 14

What is velocity?

Answer 14

Speed in a given direction

Question 15

Name 6 examples of forces

Answer 15

Pushing, pulling, twisting, friction, weight, gravity

Question 16

Name 4 benefits of friction

Answer 16

To stop things slipping. e.g A car doesn’t slip on a corner because of friction.
To stop a bicycle (friction between the brake pad and the wheel.)
To use a nail; it grips whatever it is drilled into, therefore using friction.
To let us walk without slipping. (friction between your feet and the ground
when you take a step)

Question 17

Name 4 disadvantages of friction

Answer 17

Friction causes blisters when your skin rubs off your shoe.
When you drive there is friction between the air and the car. This
wastes fuel.
Friction between the gases in the atmosphere and a space shuttle can
cause it to overheat upon re-entry. This can have disastrous
consequences.
Friction causes things to wear away; for instance the sole of your shoe
after you have been walking for a while.

Question 18

Name 3 ways of preventing friction.

Answer 18

The use of lubricants like…
Oil and grease in cars to stop things
wearing away and/or heating up.
Our joints are surrounded by a fluid that
acts as a lubricant to reduce friction.
When you lubricate the hinges on doors
it can stop them squeaking as it
reduces friction.

Question 19

A force of 10 N is being used to move an object a distance of 20 metres. Calculate the work done.

Answer 19

Answer = Work = Force by Distance
10 N X 20
Work = 200 Joules

Question 20

Calculate the work done when a force of 15 N moves an object a distance of 40 cm.

Answer 20

When calculating the work done it is important that the distance is measured in metres. In this question we change 40cm to 0.4m.

Work = Force X Distance
Work = 15 N X 0.4m
Work = 6J

Question 21

A weightlifter lifts 120 kg through a height of 2 m. Calculate the work done.

Answer 21

When lifting objects vertically the force needed is equal to the weight of the object.

Weight = Mass X 10
Force = 120kg X 10
Force = 1200 N
Therefore calculate the work use:
Work = Force X Distance
Work = 1200 N X 2m
Work = 2400 J

Question 22

A force of 10 N is being used to move an object a distance of 20m in a time of 5 s. Calculate the value of average power.

Answer 22

Work done = Force X Distance
= 10 N X 20 m
= 200 J

Power = Work
              --------
              Time
Power = 200 J
              --------
               5 s

Power = 40 watts

Question 23

A weightlifter lifts 120 kg through a height of 2 m in a time of 3 s. Calculate the average power developed.

Answer 23

We saw earlier

Work done = Force X Distance
= Weight X Distance
= 1200 N X 2 m
= 2400 J

Power = Work
——-
Time

Power = 2400 J
———–
3 s

Power = 800 watts