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# Forward force watch

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1. Hi guys, there's a worked example is A2 OCR Physics book which I don't understand. It says:
A person of mass 80 kg is sitting in a bullet train travelling on a straight level track at 80 m/s. What vertical support force and what forward force does the train provide for the person?

The answer in the book: The weight of the person is mg = 80 x 9.8 = 784 N, so the support force = 784 N upwards (resultant force zero)
Zero forward force, because velocity is constant.

I don't understand it. It says the forward force is zero, so how is the person moving if there's no forward force acting on him?
2. I know that the resultant force acting on the person is zero, because he is not accelerating, but I don't see why the forward force should be zero
3. If he is moving at a constant speed in the forward direction he does not need a force to do this. It's Newton's 1st Law.
You've answered the question yourself. There is no (horizontal) acceleration, so no resultant (horizontal) force needed.
4. If you look up Newton's first law of motion. It's because if there is no resultant force, there is no force to speed to speed it up or slow it down essentially.
5. Newtons first law states that an object at rest or moving with a constant velocity will continue to do so until a force is applied to them. Because you are inside the closed bubble of the train, there are no resistive forces acting on the person, thus no force acts on them and so they will continue to move with a constant velocity.

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Updated: October 2, 2010
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