What is conserved when two objects collide in a closed system? a)momentum b)acceleration c)speed d)velocity

The answer should be A. Momentum is a 2 objects collide in a close system. Acceleration is a rate of change in velocity. Speed is a distance it can traveled during a specific unit of time. Velocity is a displacement of an object during a specific unit of time. Velocity can be average velocity or an instantaneous velocity. Hope it helped you, and have a great day. "Thank you so much!"
-Charlie 

This is what a calorimeter is used for simpler ex, to measure calories in food.