Question

1. A 100g ball move up from ground level and come back to ground level in 10 seconds. Calculate the potential energy and kinetic energy at 8th second.

Answer 1

Solution :

Given :

m = 100 g = 0.100 kg

Here, Time total taken by the ball is 10 sec.

Therefore, Maximum height reached by the ball will be at 5 sec.

And, Initial velocity will be given by :

u = g t = (9.81 m/s²)(5 s) = 49.05 m/s

And, Maximum height reached by the ball will be :

H_max = u² / 2 g = (49.05 m/s)² / 2(9.81 m/s²) = 122.625 m

And, Potential energy at maximum height will be : PE_max = m g H_max = (0.1 kg)(9.81 m/s²)(122.625 m) = 120.3 J

.

At 8th second :

Velocity of the ball will be : v = g t = (9.81 m/s²)(3 sec) = 29.43 m/s

And, Kinetic energy at 8th second will be :

KE = (1/2) m v² = (0.5)(0.1 kg)(29.43 m/s)² = 43.3 J

And, Potential energy at 8th second will be = PE_max - KE = 120.3 J - 43.3 J = 77 J