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
Correct Answer: Option C
Explanation
Using, v2 = u2 – 2gx
(20)2 = u21/2 x 10 x 10
u2 = 600(m/s)2
initial K.E = – mu2
= (frac{1}{2}) x 600
= 30 J