## sjg13e one year ago Mass on a Pulley (involves Newton's 2nd law and friction)

1. sjg13e

question:

2. sjg13e

Question: M1 has a mass of 5.250 kg. It is on a horizontal surface, connected by a massless string to a hook where mass M2 can be increased smoothly. The pulley has a negligible mass and no friction. When M2 = 7.88kg it begins to accelerate downwards at a rate of 1.833 m/s^2. Calculate us (static friction) - uk (kinetic friction) between M1 and the surface.

3. sjg13e

|dw:1442781043086:dw|

4. sjg13e

|dw:1442781138143:dw|

5. EmmaTassone

To get the Us try to think the problem when the masses where on rest, therefore the friction equals the tension to keep the object still. On the other hand the tension to put the system in rest will be when the weight of the mass 2 equals the tension. Finally use:$F=\mu_s.N$ to get static mu.

6. EmmaTassone

to know the $\mu_k$ you have to take a similar way but now using that the sum of forces is not equal zero. $\sum_{0}^{n}F= m.a$ and the aceleration is the same for the two masses because they are linked by a string.