If you push an object with four times the work input for twice the time, your po

Question

If you push an object with four times the work input for twice the time, your power input is

twice as much

four times as much

the same

If you lift a 30 N weight vertically 40 m above the ground, you are

doing work against gravity

doing none of these

doing work against inertia

doing work against friction

Newton’s third law of motion states that the force pair acting on different objects consists of two forces that

are under the influence of gravity

always produce an acceleration

are equal and in the same direction

are equal and in opposite directions

twice as much

four times as much

the same

Explanation / Answer

1) Power is defined as work done in a unit time.

P = W/t

so if W is the original work done in time t then Power will be:

P = W/t

Now W' = 4W and t' = 2t

therefore P' = 4W/2t = 2W/t = 2P

hence P' = 2P

2) Gravity is pulling every object downwards towards the Earth so if one is lifting a weight upwards then work is being done against gravity.

3) Newton's 3rd Law states that for every action there is an equal and opposite reaction. This means that there is always a force pair acting on different objects under consideration and the two forces are equal and opposite in directions.

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