Form 3 Science Test memoranda Test 6: Force, energy ... - Pearson

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Form 3 Science Test memoranda Test 6: Force, energy ... - Pearson

Form 3 Science

Test 6: Force, energy and motion

Test memoranda

Total: 50 marks

Section A

1. B

2. A

3. D

4. A

5. A

6. B

7. D

8. C

9. B

10. A

[10]

SECTION B

11. Newton’s First Law of Motion states that an object at rest stays at rest and an

object at constant velocity continues at constant velocity unless an unbalanced

force acts on it. If an object (for example, a ball) is at rest, its velocity will be

zero. The ball will remain at rest unless someone moves it (kicks it or rolls it).

However, if the ball is moving, it will continue to move at the same velocity

unless a force acts on it (unless someone hits it or kicks it, applying a force in

the opposite direction). So, if a ball moves, stops moving or starts moving, it is

because of a force acting on it. (4)

12. Newton’s Second Law of Motion states that the acceleration of an object is

directly proportional to, and in the same direction as, the resultant force that

acts on it, and inversely proportional to the mass of the object. So, if a man

applies the same amount of force to objects of different masses, the object

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with the smaller mass will move faster. If the man applies different forces to

objects of the same mass, the object to which he applied the smaller force, will

move more slowly. (4)

13. Newton’s Third Law of motion states that for every action, there is an equal and

opposite reaction. So, when you sit in a chair, your body exerts a downward

force on the chair and the chair exerts an upward force on your body. There are

two forces that result from this interaction: a force on the chair and a force on

your body. (4)

14. F = x

F = 80 kg x 5 m/s

F = 400 m/s (4)

15. F = m x a

100 = 200 x a

=

= ½ or 0.5 m /s (4)

[20]

Section C

16. You will need a metre rule, a tennis ball and a wall. Working with a partner, one

person will throw a tennis ball while the partner marks, measures and records.

You should stand a few metres from the wall and throw the tennis ball against

the wall. Your partner should mark the spot where the ball land after bouncing

off the wall. Using the metre rule, your partner should measure the distance

from the base of the wall to the spot where the ball landed on the floor. The

distance should be recorded in centimetres. You should repeat the same

process again, throwing the ball harder. You should repeat the same process

once more, this time throwing the ball even harder.

The explanation as to why there are differences between the three distances

measured, is that the ball exerts a force on the wall. But the wall must also

exert a force on the ball because the ball was pushed back again. When the ball

is thrown lightly, it does not bounce back very far. When the ball is thrown hard

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against the wall, the ball bounces back much further. When the force of the ball

on the wall is small, the force pushing the ball back is small. When the force on

the wall is large, the force pushing the ball back is large. (10)

17. This statement is incorrect. Science is more than just a subject we learn at

school. It has a direct application to almost everything we do in everyday life.

For instance, Newton’s Laws of Motion, developed about three hundred years

ago, explain why things move fast, move slowly or stop moving.

People have used this knowledge of how forces make objects move, to make

and use machines to help them to do things. A simple machine is a tool or

device used to make work easier. We use countless simple machines in our

everyday lives. For example, a bicycle is a simple machine that helps you move

around faster than walking. Another example is a wheelbarrow that helps us

carry heavy things. Spanners, spades, tin-openers and crowbars are all

examples of simple machines that make work easier.

We also apply our knowledge of friction in our everyday lives, probably without

even realising it. For instance, we know that friction is the force that makes

moving objects come to a stop through contact with the ground. Therefore, if

we are driving on a slippery road, we know that the friction will be low and that

we must be careful. This is useful knowledge to have to prevent unnecessary

accidents. (10)

[20]

Total: 50

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Science Memo 6

© Pearson Botswana. Permission is given to photocopy these pages for school use.

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