Question

A man is loading a truck with crates that weigh 120 N each. He lifts each crate vertically through a height of 2m. a) Calculate the work done and the amount of energy spent by the man while lifting one crate. b) Calculate his power if he lifts 2 crates/minute​

Answer 1

Given:

Weight of each crane = 120 N

Height to which each crane is lifted = 2 m

To find:

1. The work done and the amount of energy spent by the man while lifting one crate.
2. His power if he lifts 2 crates/ minute.

Solution:

We know that, Work done = Force * displacement in the direction of the force

Work done in lifting one crate = Weight of the cranes * height

= 120 N * 2m = 240 Nm

Therefore work done = 240 Nm

Energy spent would be same as work done.

Therefore energy spent = 240J

Power = Work done/ time

Work done in lifting two crates = 2* work done in lifting one crate

= 2* 240 Nm = 480 Nm

Power = 480 Nm / 60 sec = 8 Nm/s = 8 watts

Therefore, power = 8 watts.