## Easy physics question

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Adam Preston
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### Easy physics question

Okay so today I started exercising Newton's laws of motion, so there was a question about a lift, a man stood in the lift who weighed 70kg, his weight which pointed downwards was shown with w, an opposing force pointing upwards was labeled r. The question was what's the value of W when the acceleration is 2m/s^2 downwards. The teacher said it was 560N, R had to be higher since it would require more force to hold the elevator. But surely if the force is higher then there would be no movement. Or does it simply mean that it accelerates for a small amount of time before the forces become equal?
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gorcee
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### Re: Easy physics question

The opposing force R pointing upwards... was it drawn against the man or the elevator?

idobox
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Location: Marseille, France

### Re: Easy physics question

In this problem, the man doesn't move relative to the lift, so the force it applies on the lift, and the lift applies to him cancel each other.
But if the lift is accelerating, you have a new vertical force applied to the man, which can also be seen as a change of the value of g, and thus a change on both the force applied by the man on the lift and the one by the lift on the man.
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Adam Preston
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Posts: 102
Joined: Sat Mar 19, 2011 10:29 pm UTC

### Re: Easy physics question

I think the force R was drawn to represent the elevator
He who will not economize will have to agonize - Confucius

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