Question

A body of mass 2 kg is thrown vertically upwards with an initial velocity of 20m/s. What will be its potential energy at the end of 2s ? ( Assume g = 10 m/s^2).

Answer 1

h=vt+1/2at^2
h=20×2 + 1/2 × (-10)2×2
h= 40 + -(20)
h=20 m

potential energy
U=mgh
U=2 × 10 × 20
U=400J

Answer 2

Given,

Mass of the body, m = 2kg,

Initial velocity, (u) = 20 m/s,

Time, (t) =2s,

Acceleration due to gravity, g = 10 m/s.

Let the height at the end of 2s = d

We know that,

d = ut + 1/2at2

d = 20 x 2 + 1/2 x (-10) x (2)2

d = 40- 20

d = 20m

(g is taken as negative because it is acting in the direction opposite to the direction of motion)

Potential Energy, P.E = mgh

= 2 × 10 × 20

= 400 J.