A2L Item 141

Goal: Reasoning with kinetic energy and work

Source: UMPERG-ctqpe58

Two
blocks, M2 > M1, having the same kinetic energy
move from a frictionless surface onto a surface having friction
coefficient μk.

Which goes further before stopping?

  1. M1
  2. M1
  3. Both go the same distance
  4. Cannot be determined

Commentary:

Answer

(1) For a given amount of kinetic energy M1 will have a larger
velocity. The penetration distance depends upon the square of the
velocity.

Many students will notice that the relationship equating the kinetic
energy to work by friction has mass as a factor on both sides and will
answer #3. They are assuming that the masses have the same velocity, not
the same kinetic energy.