A crane on a building site lifts bricks of total mass 200kg, initially at rest on the ground, with uniform acceleration. When the bricks are 5m from the ground, they have a speed of 5m/s.
How much work is done during this process?
A) 2.5kJ
B) 10kJ
C) 12.5kJ
D) 35kJ

The answer is C: 12.5 KJ

Reason:

Kinetic energy= 1/2 mv^2

= 1/2 x 2000kg x (5m/s)^2

= 2500J

= 2500/1000

= 2.5 KJ

Potential energy= mgh

= 200 x 10 x 5m

= 10,000 J

= 10,000/1000

= 10 KJ

Work done = Energy transferred Kinetic Potential = 10KJ 2.5KJ = 12.5 KJ

the answer is b ) square root of 5