Question

A ball of mass 200g is thrown vertically upwards with a velocity of 30m/s. What will be its kinetic energy after 5 seconds?
1) 40j
2) 190000j
3) 1209j
Please provide full solution

Answer 1

the height travelled by the ball in 5sec = ut +1/2at^2

= 30×5 -1/2×10×25. ( as g=-10)
=150-125
=25m

the potential energy gained = kinetic energy lost
mgh = kinetic energy lost
=0.2×10×25
=50J

initial kinetic energy = 1/2×m×v^2
= 1/2×0.2×900
=90J
kinetic energy after 5sec = initial kinetic energy - lost kinetic energy
= 90-50=40J


therefore the answer is 1)

Answer 2

The correct answer is (90-50) J = 50 J.