Question

The momentum of a body is decreased by 20% How many percentage will the kinetic energy is decreased

Answer 1

Explanation:

If the momentum of a body is decreased by 20% its kinetic energy is decreased by 36%.

when momentum is still unaltered it is p = mv

when it decreased by 20 % the resulting new value is 80% of the original that is p-p’ =

p - 0.2p = mv - m 0.2v = m(v-0.2v) = m * v * 0.8

When KE is still unaltered it is KE = 1/2mv^2.

Applying the new value of v as 0.8v the new KE’ = 1/2 m * (0.8v)*2

The new KE’ = 1/2m * 0.64v^2

The resulting (KE)’ = 1/2mv^2 - 1/2m * 0.64v^2 = 1/2m * 0.36v^2

The decreased in its KE is 36%

Answer 2

Ek =1/2mv^2
M is reduced by 20 % so new m =0.8 m
Ek = 1/2 *.8m v^2
So kinetic energy is also reduced by 20%