Physics - NEWTON's first law and related?

Question

A high tech jet car speeds along the desert floor at a constant velocity of 180 miles/hr north.a) what is the net force on the jet car?
the jet car hits some sand which causes a drag force on the car of 5000 N to the south. The computer instantly compensates so the jet exerts a thrust force on the car of exactly 5000 N to the north at the same time the car hits the sand. The jet car now... choose ALL that apply:
slows down
remains at rest
maintains constant velocity
moves with constant non-zero velocity
speeds up
moves with a changing velocity
accelerates at a constant rate

Newton's first law states: When the ____ on an object is zero, the object will ____ constant ____.
Another way of saying this is that, if the total force on it equals zero, an object's ___ will also be zero.

Is it necessary to apply a force to keep an object going in a circle at constant speed?
Yes/No, because the ____ is changing/not changing.

Answer 1

OK, I'll try to help you learn the principle so you can pass the test. My explanations are in ().

A high tech jet car speeds along the desert floor at a constant velocity of 180 miles/hr north.a) what is the net force on the jet car? the jet car hits some sand which causes a drag force on the car of 5000 N to the south. The computer instantly compensates so the jet exerts a thrust force on the car of exactly 5000 N to the north at the same time the car hits the sand. The jet car now... choose ALL that apply:

(There has been drag all along. Since the car has been going at a constant velocity, the car's jet has to be exerting an equal and opposite force to compensate for the drag. If the drag and thrust are equal and opposite there's no net force. Newton's 1st says it will stay in motion at the same speed in the absence of a net force. So now, the net force = 5000 N - 5000 N = 0.) The car

maintains constant velocity
moves with constant non-zero velocity

(I explained all this above.)
Newton's first law states: When the __ net force__ on an object is zero, the object will __maintain__ constant __velocity__.
Another way of saying this is that, if the total force on it equals zero, an object's _acceleration__ will also be zero.

Is it necessary to apply a force to keep an object going in a circle at constant speed?

(The object will want to keep going at constant speed in a straight line because of inertia - without a net force it will do that. The force required to go in a circle is towards the center.)

Yes, because the __velocity__ is changing.

Answer 2

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