SAT Subject Physics Practice Question 519: Answer and Explanation

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Question: 519

5. A spring accelerates a 2 kg cart from rest in a time of .8 seconds, giving it a momentum of 4 kg·m/s. With what force did the spring accelerate the cart?

A. .5N
B. 1.6N
C. 3.2N
D. 5N
E. 8N

Correct Answer: D


The correct answer is (D). The impulse impressed onto the cart is the same as the momentum the cart achieves. The momentum is given as P = mv, which was given to the cart in a time of .8 sec. The impulse an object receives in a given time is Ft = ΔP. The solution is found by replacing the P (momentum), yielding the equation Ft = mv, which is rearranged to find the force. F = (m)(v)/t.

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