Circular Motion of bicycle wheel

[Asher242]

Homework Statement

A bicycle wheel has a radius of 0.5 m. When it spins, it completes one full turn in 1.6 s. Two identical rocks are stuck on the wheel at a radius of 0.4 m and 0.2 m. What is the ratio of the force on the outer rock to that of the inner rock?

Homework Equations

F=ma
F=mw^2r
F= (mv^2)/r
These are the only formula's I believe could be relevant

The Attempt at a Solution

I've looked at both f=(mv^2)/r and f=mw^2r but I just can't get it. I don't understand how I'm supposed to find the force with on the time and the radius. This led me to believe that I don't have to necessarily solve it but after that I'm lost

 

[ehild]

Homework Statement

A bicycle wheel has a radius of 0.5 m. When it spins, it completes one full turn in 1.6 s. Two identical rocks are stuck on the wheel at a radius of 0.4 m and 0.2 m. What is the ratio of the force on the outer rock to that of the inner rock?

Homework Equations

F=ma
F=mw^2r
F= (mv^2)/r
These are the only formula's I believe could be relevant

The Attempt at a Solution

I've looked at both f=(mv^2)/r and f=mw^2r but I just can't get it. I don't understand how I'm supposed to find the force with on the time and the radius. This led me to believe that I don't have to necessarily solve it but after that I'm lost

You need the angular speed, w. The wheel completes a full turn in 1.6 s. What angle is a full turn? What is the angular speed then?

 

[Asher242]

Thank you so much for helping me :D

So going off of what you said I found the angular velocity to be 3.9ms (using w=2*pi*f) and from that I can also find the velocity of both of the rocks, however to find the force using either F=(mv^2)/r or F=mw^2r I would need the mass as there would be two unknown variables. Do I make up my own mass? (I've seen my teacher do it before) but, if everyone constructs their own mass it would be impossible to get the same answer right? Or, am I using the wrong formulas...

 

[Bandersnatch]

I found the angular velocity to be 3.9ms (using w=2*pi*f)

Your units are incorrect here.

But more importantly, pay attention to the bit of the question that requires you to find the ratio of two forces.

Write down the force equation for each rock separately, without plugging in any numbers. Just the symbols.
The question asks you to find $F_1/F_2$. See if any variables cancel out.