Question

Akhshay is a student of class 9. He was waiting for a bus on a bus stand. He saw an old man trying to keep his luggage on the roof of the bus and unable to do it. Akhshay picked up his luggage and placed it on the roof of the bus. The old man thanked Akshay for the same. What is the equation for work done against gravity?

Answer 1

Work done is given by:
W = F.s
where F is the force acting
s = displacement
Here, the force will be the weight of the luggage. Therefore F = mg, acting in a downward direction.
s = height of the bus, displacement is in an upward direction
Therefore, W= -Fs
The negative sign shows that the force of gravity is acting in a direction opposite to the direction of displacement.