Answer:
C. bowling balls
D. steel cubes
Step-by-step explanation:
You want to identify the elastic collisions from the list ...
- a car collision where the cars stick together
- a ball of sticky tape hitting a billiard ball\
- two bowling balls of equal mass
- two steel cubes on a friction-less surface (no energy loss)
Elastic collision
An elastic collision is one in which there is no loss of kinetic energy. Both kinetic energy and momentum are conserved.
In general, a collision is not elastic if energy is dissipated as sound, light, heat, or deformation of material.
Choices
Of the offered choices, the first two (car collision, sticky tape collision) will result in deformation of one or more of the colliding objects. That deformation dissipates energy, so the kinetic energy after the collision will be different from before the collision.
The collision of (C) bowling balls, and (D) steel cubes are elastic collisions. Neither results in deformation of the colliding objects.
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Additional comment
Clearly, any sort of collision can be engineered with enough starting energy to cause the colliding objects to disintegrate. Here, we're primarily concerned with collisions that allow the integrity of the colliding objects to be maintained (except in crashed cars).
The collisions are more or less assumed to be "ideal" in that there is no significant energy loss due to sound or vibration of the objects involved.