Question

A bird flying at a height of 12 m doubles its speed as it descends to a height of 6.0 m. The kinetic energy has changed by a factor of : a) 2 b) 4 c) 1 d) 0.25

Answer 1

Answer:

Option d)

Explanation:

As the Kinetic energy of the body ids due to the speed of the body and depends on it, it does not depend on the height of the body.

The kinetic energy is given by:

KE = $\frac{1}{2}mv^{2}$

where

m = mass of the body

v = kinetic energy of the body

Now, as per the question:

Initial velocity is u

and final velocity, v = 2u

Thus

Initial KE = $\frac{1}{2}mu^{2}$               (1)

FInal KE = $\frac{1}{2}mv^{2}$ = $\frac{1}{2}m(2u)^{2}$          

FInal KE = 4$\frac{1}{2}mu^{2}$               (2)  

Thus from eqn (1) and (2):

Final KE = 4(Initial KE)

The Kinetic Energy has changed by a factor of 4