Question

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

Answer 1

Mass of body=2kg
initial vel=20 m/s
final vel=?
time =2s
g=10m/s²
v=u +gt (by 1st equation)
v= 20 + 10*2
v=40 m/s
Now, p=mv (p= momentum)
p= 2*40
=80 kg m/s
Hence, kinetic energy =80 kg m/s

Answer 2

Mass of object = 2 kg
Initial velocity = 20m/s
Time = 2s
Object is thrown vertically upwards so the g = -10m/s²

From equation
v = u + gt we get
v = 20m/s + (-10m/s²) × 2s
v = 20 - 20
v = 0m/s

K.E. = (1/2mv²) - (1/2mu²)
K.E = (1/2×2×0) - (1/2×2×400)
K.E. = (0) - (400)
K.E. = -400kgm²/s²

The Kinetic energy of the object will be 400kgm²/s².

I hope this will help you out with your problem.