Three physics students discussing this situation make the following statements:

Question

Three physics students discussing this situation make the following statements:

ALEX: "These carts will both be at rest after the collision since the initial momentum of the system is zero, and the final momentum has to be zero also."

BELINDA: "No, that would mean that they would have zero kinetic energy after the collision and that would violate conservation of energy. Since the right hand cart has more kinetic energy, the combined carts will be moving slowly to the left after the collision."

CHANO: "No, you are both wrong. The pair of carts will be traveling left at 20 cm/s. That way conservation of momentum and conservation of energy are both satisfied."

Alex is correct. Can you explain why he is correct??

In the figure, two carts traveling in opposite directions are about to collide. The carts are identical in size and shape, but they carry different loads and are initially traveling at different speeds. The carts stick together after the collision. Three physics students discussing this situation make the following statements: ALEX: These carts will both be at rest after the collision since the initial momentum of the system is zero, and the final momentum has to be zero also. BELINDA: No, that would mean that they would have zero kinetic energy after the collision and that would violate conservation of energy. Since the right hand cart has more kinetic energy, the combined carts will be moving slowly to the left after the collision. CHANO: No, you are both wrong. The pair of carts will be traveling left at 20 cm/s. That way conservation of momentum and conservation of energy are both satisfied. Alex is correct. Can you explain why he is correct??

Explanation / Answer

There is no external force on the 2 cart system.

[ Although each cart may exert force on the other ]

since there is no external force , the momentum is conserved.

so initial mometum = final momentum ;

or 20 * 8 - 40 * 4 = ( 20 + 40 ) V

or V = 0 <----------ans

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