- #1

anonymous99

- 25

- 5

- Homework Statement
- A spool with inside radius R1 =80mm and outer radius R2= 160mm rolls without slipping on a rough horizontal surface. Mass of spool =5kg and moment of inertia = 0.072kg m^3. A wire is wound round the inner radius and a force, F, of 20N is applied horizontally to the right. Calculate the linear/angular accelerations of the spool.

- Relevant Equations
- Sum of forces in x direction= F - Fr where Fr is friction force on the rim.

Sum of torques = F*R1 - Fr*R2 = I*a/R2

I did some substitution and rearranging to get rid of Fr and got F*R1-F*R2 = a(I/R2 - M*R2) which gives a= 4.57 ms^-2 which is wrong. If i take clockwise torque as positive instead, I get -F*R1+Fr*R2= I*a/R2 which rearranges to F*R2-F*R1 = a(I/R2 + M*R2) which gives me the right value of 1.28.

Shouldn't the answer have the same magnitude regardless of sign convention?