Grade 8 - Learning



Grade 8

Science Test – Force, Work, energy and Power

w = mg g = 10 W = Fd [pic]

1. Multiple choice questions – write down the number of the question and the letter of the correct answer next to it

1.1 A car is pushed 300 m in 500 seconds by a horizontal force of 200 N applied in the direction in which the car is moving. The work done in kilojoules is

A [pic]

B 300 x 200 x 500

C [pic]

D 300 x 200 (2)

1.2 The power in watts in question 1.1 is

A 300 x 200 x 500 B [pic]

C [pic] D [pic] (2)

1.3 An object has a mass of 4kg on the moon. Its weight and mass on the earth will be

A. 240N and 24kg

B. 240N and 4kg

C. 40N and 4kg

D. 40N and 24kg (2)

2. True / False Simply write down true or false for each question

2.1 Whenever work is done there is always an energy transfer.

2.2 The two conditions for work to be done are a force and movement in any direction by the

object on which the force is exerted.

2.3 The unit of work is the Newton.

2.4 The ability of an object to perform work because of its position is called kinetic energy.

2.5 At a hydro-electric power station the kinetic energy of the falling water is converted to

electric potential energy. (10)

3. State the type of energy conversion in each of the following:

3.1 The brakes of a car are applied

3.2 A person rubbing his hands together

3.3 An object that falls to the earth from a certain height

3.4 A compressed spring is released. (8)

4. What is a force? (2)

5.1 State the Law of Conservation of Energy. (3)

5.2 State the definition of power. (2)

6. Name the type of potential energy stored in each of the following

6.1 A bow about to fire an arrow

6.2 Water at the top of a waterfall

6.3 A birthday cake (3)

Calculations

7. A boy lifts an object of 2,5 kg through a height of 3 m in 0,5s. Calculate the:

7.1 weight of the object. (4)

7.2 work done. (4)

7.3 power. (4)

8.1 Calculate the work done by the man, shown in the diagram below, pushing the trolley

by applying a force of 30N for 150 m. (4)

8.2 Calculate his power if the man covers the distance of 150m in 30 seconds. (4)

9. A man, mass 95kg, wants to climb a flight of stairs, 15m high. Assume an average apple

provides 20kJ of energy. How many apples are required to perform this task. (6)

TOTAL : 60 MARKS

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