Question

an object of mass m and velocity v has kinetic =200j find the new kinetic energy if the mass of the object becomes double and velocity still remains the same.

Answer 1

let the k.e. in first case be x
x = 1/2*m*v^2=200j
in second case
let the kinetic energy be x'
v'=v
m'=2m
x'= 1/2*2m*v^2
x'= 2(1/2*m*v^2)
x'=2(x)
x'=2*200j
x'=400j

Answer 2

kinetic energy ($K_{e}$) of an object with mass m  and velocity v=$\frac{1}{2}$m$v^{2}$=200J(given)
when mass becomes double,then, m=2m
now $K_{e}$=$\frac{1}{2}*2mv^{2}$
200J=$\frac{1}{2}*2mv^{2}$$\frac{200}{2J}$=$\frac{1}{2}*mv^{2}$
100J=$\frac{1}{2}*mv^{2}$
∴ new $K_{e}$=100J