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A2L Item 138

Meta-Information
Description: 
Determine the velocity of a block before a collision from information about the final state of the system.
Goal: 
Problem solving with momentum
Level: 
Undergraduate
Keywords: 
Conservation
Keywords: 
Friction
Keywords: 
Mechanics
Keywords: 
Momentum
Source: 
UMPERG-ctqpe46

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?

  1. 2 m/s
  2. 4 m/s
  3. 6 m/s
  4. 8 m/s
  5. 12 m/s
  6. None of the above
  7. Cannot be determined
Commentary

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.