Question

In loading a truck, a man lifts boxes of 100 N each through a height of 1.5 m. (g = 10 m s⁻²)

1. How much work does he do in lifting one box?
2. How much energy is transferred when one box is lifted?
3. If the man lifts 4 boxes per minute, at what power is he working?

Answer 1

Given:

Weight of box, (W) = 100 N

Height, (h) = 1.5 m

Acceleration due to gravity, (g) = 10 m/s²

(i) Work done (W) in lifting an object vertically is the product of the upward force (equal to the weight of the object) and the vertical height. 

Work done = Weight × h

= 100 N × 1.5 m

= 150 J

(ii) By the Work-Energy Theorem, the work done on the box is entirely converted and stored as gravitational potential energy in the box.

Energy Transferred = Work Done on one box

Energy Transferred = 150 J

(iii) Since he lifts 4 identical boxes, the total work is:

W_total = 150 J × 4

= 600 J

Time taken, (t) = 60 s

Power = `"W"_"total"/t`

= `(600  J)/(60  s)`

= 10 W

So, the power is 10 W.