Question

If an object weighs 500N and you lift it 2m how much work have you done on it?

Answer 1

Hint: As you are lifting the object you are doing work on the object. The work W done on an object by a constant force is defined as $ W = F \cdot h $ . It is equal to the magnitude of the force, multiplied by the height of the object lifted in the direction of the force. The SI unit for work is the joule (J), or $ Nm $

Complete step by step answer:
Work done in lifting an object vertically by the height h is given by
 $ W = F \cdot h $
Where $ F $ is the force exerted by the body and $ h $ is the distance by which it is lifted.
Now the force exerted by the body is in the direction of gravitational force and hence is given by
  $ F = m \cdot g $ And is given that is
 $ F = 500N $
Also we have given that,
Height through which the body is lifted is, $ h = 2m $
So the Work done on lifting the body will be
 $ W = F \cdot h $
 $ \Rightarrow W = \left( {500N} \right) \cdot \left( {2m} \right) $
Solving further we get,
 $ \Rightarrow W = 1000Nm $
i.e.
 $ \Rightarrow W = 1000J $
Hence the work done in lifting the object of weight $ 500N $ by $ 2m $ is equal to 1000J.

Note:
If work is done on the system, its sign is positive. If work is done by the system, its sign is negative. Here work is done on the system and hence it is positive. The error might occur in distinguishing mass and weight, Weight is the force exerted by the mass. If their mass is given instead of weight then we have to get the force exerted by the object by multiplying the mass with the acceleration due to gravity i.e. $ g $ .