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Newtonian Mechanics

 
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CBR600F



Joined: 12 Mar 2012
Posts: 1
Location: UK

PostPosted: Wed Mar 14, 2012 9:07 pm    Post subject: Newtonian Mechanics Reply with quote

Sorry if this question seems remedial. I'm trying to learn physics for fun in my own time. But this has had me stumped for too long. I'm not sure how I'm supposed to work it out.

The answer is 5.0kg. I know because I looked in the back of the book. I just can't figure out the methodology. The examples leading up to this question don't involve spring balances.

Q. A body hangs from a spring balance which is suspended from the ceiling of a lift. What is the mass of the body if the balance registers a reading of 70N when the lift has an upward acceleration of 4.0 ms^-2? (g = 10ms^-2).

I know by Newton's Second Law that F = ma, and so 70 = m/4.0, and therefore m = 70/4.0 = 17.5kg. But I know that this is based of an 'artificial' weight caused by upward acceleration, and is not the body's actual mass.

Please help.
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