Question

If kinetic energy of a body is reduced to 30% of initial, by
slowing it down. Then the final velocity is approximately
..........%of the initial velocity
a)55%
b)50%
c)45%
d)66%​

Answer 1

Answer:

a

Explanation:

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Answer 2

Given:  Kinetic energy is reduced to 30% of initial

To Find: Final velocity is what percent of initial

Solution:

Let initial kinetic energy be K

Let initial velocity of the body be u

Let final kinetic energy be K'

Let final velocity be v

Kinetic energy of the body is given as

KE = $\frac{1}{2} mv^{2}$ where m is the mass of the body and v is the velocity of the body

K = $\frac{1}{2} mu^{2}$ and K' =$\frac{1}{2} mv^{2}$

We know that  kinetic energy is reduced to 30% of initial

So, K' =  $\frac{30}{100}$ K

K' = 0.3 K

$\frac{1}{2} mv^{2}$   = 0.3 $\frac{1}{2} mu^{2}$

$v^{2}$ = $\frac{3}{10} u^{2}$

$\frac{v}{u}$ = $\sqrt{\frac{3}{10} }$

$\frac{v}{u}$  = 0.547

$\frac{v}{u}$ x 100 = 55%

Therefore, the final velocity is approximately a) 55% of the initial velocity.