Question

If momentum of an object is increased by 10% then its kinetic energy will increase by a) 20% b) 21% c) 40% d) 19%

Answer 1

It will be increased by 21%
Let the initial mass of the body be m and its velocity be v. 
Initial momentum of the body = mv 
Initial KE = mv^2/2 
If the momentum increases by 10%, new momentum = mv + 10% of mv 
= mv + 10/100mv 
= mv + mv/10 
=11mv/10 
=m(11v/10) 
New velocity = 11v/10 
Increase in velocity = v/10 
New KE = m(11v/10)^2/2 
= 121/100mv^2/2 
Increase in KE = 21%

Answer 2

Increase in KE =[(200+-n)n]÷100

n=%increase or % decrease

Here n =10

So increase in KE = [(200+10)×10]÷100

=2100÷100 = 21%