Calculate the magnitude of the force exerted by the spring

[MusicMonkey]

Calculate the magnitude of the force exerted by the spring on mass Mb=300g, moving in a circle of radius r=22cm. The mass makes 10 revolutions in 4 seconds. Determine the mass m, suspended over the pulley which stretch the spring by the same amount as during the rotation.

For the magnitude of the force I used the equation V=2(pi)f*r. Then I plugged in f=4/10 and r=22 cm. Then I used F=mv^2/R and calculated for Force. Is this correct?

For the second part of the question I do not understand how to do it.

 

[BLaH!]

Yep, it sounds like you did the first part correctly. For the second part you will need to remember the relation between the spring force and the extension of the spring. That is,

F_{spring} = k\Delta x

From the first part of the problem

k\Delta x = M_b\frac{v^2}{R}

(Of course you don't even need to know what k or \Delta x are to do the first part.)

In the second part you have a mass m that is being suspended by the spring. Thus,

F_{spring} = k\Delta x' = mg

The problem states that \Delta x' = \Delta x. Thus,

k\Delta x' = k\Delta x = M_b\frac{v^2}{R} = mg

Now just solve for m.

 

[wais]

Your calculation for the magnitude of the force exerted by the spring on mass Mb=300g is correct. However, the mass m suspended over the pulley cannot be calculated using the given information. In order to determine this mass, we would need to know the spring constant and the amount of stretch in the spring caused by the rotation of the mass Mb. Without this information, it is not possible to accurately calculate the mass m.