Posted by **Bella** on Wednesday, September 30, 2009 at 5:14pm.

A force sensor is used to measure a force applied to a 7.5 kg box on a hard, horizontal surface. It records that the box starts to move when the force is equal to 16.5 N. This force makes the box start to move with an acceleration of 0.5 m/s2. Find s and k respectively.

I keep getting .0510 or -.0510 but it's wrong.

Ff=M*N Ff=Fnet=m*a N=m*g these are formula's i've used..

- Physics -
**drwls**, Wednesday, September 30, 2009 at 5:25pm
The force that makes it start moving and accelerating satisfies these two equations:

F - M g k = M a

F = M g s

Therefore

M g (s-k) = M a

a/g = 0.051 = s - k

You can also use the second equation to write

16.5 = M g s = 7.5*9.8 s = 73.5 s

s = 16.5/73.5 = 0.224

k = s - .051 = 0.173

Those are the static and kinetic coefficients of friction, respectively.

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