Posted by **Dani** on Tuesday, March 13, 2012 at 5:29pm.

In this problem they show a diagram of a pulley system with an inclined plane (25 degree incline). There is a box called m1=47kg resting on the incline plane and m1=35kg hanging on the vertical line. The question reads: The coefficient of friction between m1 and the surfvace of the inclined plane are Ustatic=0.42 and Ukinetic=0.19.

a)if the masses are held in place and then released , will they start to move? ------> I know the answer is NO.

b)how much mass would you have to add to m2 to cause the masses to begin to move? ----> The answer should be 2.8kg but I dont know how the book got this answer.

c)If you said no to a) and added the mass that you calculated in b), what would be the acceleration of the masses? ---> answer given in the back of textbook is 5.7 m/s^2

ANY help with this problem would be greatly appreciated!! THANK YOU SO MUCH in advance :)

- Physics -
**Henry**, Wednesday, March 14, 2012 at 9:46pm
W1 = m1g = 47kg * 9.8N/kg = 461 N

W2 = m2g = 35kg * 9.8N/kg = 343 N.

F1 = 461N @ 25 Deg.

Fp = 461*sin25 = 195 N.=Force parallel

to the incline.

Fv = 461*cos25 = 418 N. = Force perpendicular to incline.

Fn = F2 - Fp - Fs.

Fn = 343 - 195 - 0.42*418 = 0.

Fn = 343 - 195 - 176 = -28 N.

a.No, the masses would not move, because the opposing force is 28 N greater than F2. Therefore we must add

28 N. to F2:

b. mg = 28 N.

m = 28/g = 28 / 9.8 = 2.86 kg added.

- Physics -
**anonymous**, Thursday, March 15, 2012 at 10:13am
thank you very much! and to find the acceleration would it just be Fnet=ma and solve for a... Fnet=Fg-Ff?

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