An iron block of mass 4kg is initially on the ground. A worker lifts it straight up to a platform 3m high, then further up to a balcony 6m high, and finally lets it down gently onto a cart that is 2m above the ground.
a. (a) Calculate the total work done by the worker against gravity during the two upward lifts.
b. (b) Determine the net change in the block’s gravitational potential energy between its initial position on the ground and its final position on the cart. Take g=9.8m/s2.