Problem 10: A force of 2000 N is exerted in lifting a 100 kg mass straight up to a height of 10 m.

• How much work is done?
• What are the K.E and P.E of the object when it gets to that height?

Solution

Theory: When force is exerted on the body to lift it, work is done which is equal to the sum of the P.E and K.E of the body. So we calculate the work done on the body, and after that, find the P.E and K.E.

• Given:      Mass of the body, m = 100 kg,                  Force applied, F = 2000 N

                              Distance, h = 10 m

Find:                     Work, W

Formula               W = Fh

Put the values,   W = 2000 × 10 = 20000 J = 20 KJ

• This work is converted to the P.E and K.E of the body. Therefore,

W = P.E + K.E     …     (A)

P.E = mgh = 100 × 9.8 × 10 = 9800 J

Put the values of W and P.E in equation (A)

20000 = 9800 + K.E      OR      K.E = 20000 – 9800 = 10200 J = 10.2 KJ