In a lab, two identical lab carts (m = 1.0 kg) travel toward each other, each with a speed of 2 m/s. The cars collide, and one cart moves to the right with a speed of 3 m/s and the other moves left with a speed of 2 m/s.
Answer
T
This experiment did not occur in a closed system.
T
This proves the conservation of momentum since pi = pf .
A
An additional mass was added to one cart, which explains the increase in speed.
T
The increase in speed was due to the kinetic energy from one cart transferring to the other.
Explanation
Take right as positive. The initial total momentum is (1.0 kg)(+2 m/s) + (1.0 kg)(−2 m/s) = 0, but the final total is (1.0 kg)(+3 m/s) + (1.0 kg)(−2 m/s) = +1 kg·m/s. Since momentum changed, the collision as described cannot have occurred in a closed system; an external force or impulse must have acted. The correct choice is A, “This experiment did not occur in a closed system.”
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