Question

A ball of mass 3 kg is thrown upwards with a speed of 10 m/s. When the ball reaches the highest point, the work done on it by the gravity will be

• A. 300 J
• B. -150 J
• C. -300 J
• D. 150 J

Answer 1

The correct option is B -150 J

Given,
Mass of the ball, m = 3 kg
Initial velocity, u = 10 m/s
At the highest point, the velocity of the ball will be zero.
So, final velocity, v = 0 m/s

We know that,
$v^2=u^2+2as$
$0={10}^2-2\ast 10\ast s$
$s=\frac{100}{2\ast 10}$
$s=5m$

So, work done by gravity = Force x Displacement = mgh = 3 x -10 x 5 = -150 J