Object A has of mass 7.20 kilograms, and object B has a mass of 5.75 kilograms. The two objects move along a straight line toward each other with velocities +2.00 meters/second and -1.30 meters/second respectively. What is the total kinetic energy of the objects after the collision, if the collision is perfectly elastic?

Question

anonymous · Answer

Please show me HOW to get your answer!
My choices are:


19.3 joules
21.9 joules
38.5 joules
43.0 joules
50.8 joules

anonymous · Answer

okay, so the momentum changes because an outside force is applied...

anonymous · Answer

wait! the momentum is the same amount, I just have to figure out how it shifts.

anonymous · Answer

KE=0.5 * mv^2, right?

anonymous · Answer

then add the 2 together?

anonymous · Answer

as the collision is elastic kinetic energy of the system will be conserved and it will be equal to total initial kinetic energy 
=.5*7.2*2*2 + .5*5.75*1.3*1.3

anonymous · Answer

thank you! 

I got 14.4+4.85

Whick rounds up to A) 19.3 :)