Question

In compressed state, a spring 3.00 meters long hanging from the ceiling has a potential energy of 2.0 joules. If the entire potential energy is used to release a ball of mass 1.2 kilograms vertically downward, then what is the kinetic energy of the ball when it reaches the ground?
a) 1.2 joules
b)4.9 joules
c)2.0 joules
d)6.8 joules

Answer 1

The correct option is: Option (C) 2.0 Joules.

Explanation:

According to law of conservation of Energy:

Initial Energy = Final Energy
KE(initial) + PE(initial) = KE(final) + PE(final) --- (1)


When in the compressed state:
KE(initial) = Initial Kinetic Energy = 0
PE(initial) = Initial Potential Energy = 2.0 J

At ground (since height is 0 with respect to ground)
KE(final) = Final Kinetic Energy
PE(final) = Final Potential Energy = 0.0 J

Plug all in (1):
(1) => KE(final) = 2.0 J (Option C)