A2L Item 138
- Description: Determine the velocity of a block before a collision from information about the final state of the system.
- Goal: Problem solving with momentum
- Source: UMPERG-ctqpe46
- Keywords: Conservation, Friction, Mechanics, Momentum
The question for students:
A
block slides along a frictionless surface and onto a slab with a rough
surface. The plot on the right shows the velocity of the blue slab as a
function of time. The slab has mass of 4kg and the block has mass of
2kg. If the block remains on top of the slab, what was its initial
speed?
- 2 m/s
- 4 m/s
- 6 m/s
- 8 m/s
- 12 m/s
- None of the above
- Cannot be determined
Commentary for teachers:
Answer
(6) The block initially has velocity 3 m/s. This problem is difficult for students. They generally have difficulty obtaining relevant information from a diagram. In this case they must use the plot to tell that the final velocity is 1 m/s.