A $620-$g object traveling at $2\mathrm{.}1$ m$/$s collides head$-$on with a $320-$g object traveling in the opposite direction at $3\mathrm{.}8$ m$/$s$.$ If the collision is perfectly elastic, what is the change in the kinetic energy of the $620-$g object?

hint: Before the velocity is negative for one of the mass. you don't need to convert g to kg $.$ After the collision the relative velocity is the same'$($with negative velocity$).$

So V$1-$V$2=$ V$2\text{'}-$ V$1\text{'}=2\mathrm{.}1-(-3\mathrm{.}8)=5\mathrm{.}9=$ V$2\text{'}-$ V$1\text{'}($conservation of KE$\_$

and m$1$V$1+$m$2$V$2=$ m$1$V$1\text{'}\_$m$2$V$2\text{'}($conservation of momentum$)$

Find V$1\text{'}$ and V$2\text{'}$ then change $=0\mathrm{.}5$ m$1$ V$1\text{'}2-0\mathrm{.}5$ m$1$ V$12$

Group of answer choices

It loses $0\mathrm{.}47$ J$.$

It doesn$$t lose any kinetic energy because the collision is elastic.

It loses $1\mathrm{.}4$ J$.$

It gains $0\mathrm{.}69$ J$.$

It loses $0\mathrm{.}23$ J$.$