(b) -mgh
Reason — When a ball m is thrown upwards to a height h, the displacement h (upwards) is opposite to the direction of force of gravity mg (downwards), so the work done by the force of gravity mg in displacement h is W = -mgh i.e., negative.
Question
When a ball m is thrown upwards to a height h, the work done by the force of gravity is: (a) mgh (b) -mgh (c) mg (d) mgh2
WhatsApp
💡 Some Related Questions
The diagram given below shows a ski jump. A skier weighing 60kgf stands at A at the top of ski jump. He moves from A and takes off for his jump at B. 
(a) Calculate the change in the gravitational potential energy of the skier between A and B. (b) If 75% of the energy in part (a) becomes the kinetic energy at B, calculate the speed at which the skier arrives at B.(Take g = 10 ms-2).
Open Answer »
A metal ball of mass 2kg is allowed to fall freely from rest from a height of 5m above the ground. Taking g = 10ms-1, calculate: (a) the potential energy possessed by the ball when it is initially at rest. (b) the kinetic energy of the ball just before it hits the ground? (c) What happens to the mechanical energy after the ball hits the ground and comes to rest?
Open Answer »Show that the sum of kinetic energy and potential energy (i.e., total mechanical energy) is always conserved in the case of a freely falling body under gravity (with air resistance neglected) from a height h by finding it when(i) the body is at the top,(ii) the body has fallen a distance x,(iii) the body has reached the ground.
Open Answer »