Question

A weightlifter lifts a 1250N barbell 2m in 3s.How much power was used to lift the barbell

Answer 1

Work done is equal to the force applied multiplied by the distance moved in the direction of the force. The weight force acts vertically downwards and the distance moved is vertically upwards so they are in the same line. Hence W = Fx = 1250 * 2 = 2500J. Power is the rate of work done, i.e. work done divided by time. P = W/t = 2500/3 = 833W (3sf)

Answer 2

Work = (force) x (distance)

         =  (1,250 N) x (2 m)  =  2,500 N-m  =  2,500 Joules

Power = (work)  /  (time to do the work)

           =  (2,500 J) / (3 sec)  =  2500/3  J/s  =  833-1/3 watts

                                                                   (1.12 horsepower)