An object of mass 100g projected vertically upwards from the ground level has a velocity of 20ms\(^{-1}\) at a height of 10m. Calculate its initial kinetic energy at the ground level.[g = 10ms\(^{-2}\), neglect air resistance]
A
10 J
B
20 J
C
30 J
D
50 J
Verified Correct Answer: C.
Physical Principles & Numerical Solution
Using, v\(^2\) = u\(^2\) - 2gx
(20)\(^2\) = u\(^2\) - 2 x 10 x 10
u\(^2\) = 400 + 200 = 600(m/s\(^2\))
initial K.E = \(\frac{1}{2}\)mu\(^2\)
= \(\frac{1}{2}\) x 0.1 x 600
= 30 J
(100g = 0.1kg)
Source: Myschool Past Questions Archive (Record #27685)