In an earlier activity in class you worked with a fan-powered friction-cart, wit

Question

In an earlier activity in class you worked with a fan-powered friction-cart, with its pad slightly lowered. You saw that its speed increased as it moved along the track. However, you now know that, because of the effects of the drag force, eventually this cart would indeed reach a constant speed, if the track were long enough.

Now suppose you took this setup (including an extremely long track) to the Moon, which has no atmosphere. You replace the fan with a tiny rocket motor that pushes with the same strength (a fan needs air to work!) and lower the fricition pad slightly. When you release the cart at one end of the track it starts to move.

Assuming the rocket does not run out of fuel, what would the motion of the cart be like as it moves further and further along your extremely long track?
Question options:
A) It would eventually reach a constant speed, because the net force acting on it would decease in strength as it speeds up.
B) After initally speeding up, its speed would quickly become constant because only the force of the rocket is acting on it. There would be no kinetic friction because there is no gravity on the moon to hold the cart on the track.
C) It would just keep speeding up at the same rate, because the net force acting on it would remain constant.

Explanation / Answer

a) no, the net force will not decrease. b) no, if the only force acting on the cart was the rocket, then the system would continue to accelerate as the force would cause a constant acceleration. c) yes. there is drag force is negated so only rocket and friction cause force

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