Tension and acceleration of a pulley sytem attached to a block

  • Thread starter emmaemma08
  • Start date
  • #1
A 10kg block is attached to a massless cord that doesnt stretch or sag which is wrapped around a disc-like wheel for which m=5kg, I=(1/2)mR^2. If the block is allowed to drop straight down held back only by the rotation of the wheel
a) What is the tension in the rope
b) What is the acceleration of the block

I know that the tension isnt just F=mg and so am thinking it is combined with the mass of the block but dont know how to go about it
 

Answers and Replies

  • #2
LowlyPion
Homework Helper
3,090
5
Welcome to PF.

Consider the torque on the wheel.

What equations do you know for Torque?
 
  • #3
I know that torque = r x F or rFsintheta
i think it needs to use the ones related to angular momentum where torque= dL/dt= Id omega/ dt= I alpha
there was a similiar question but it just said the things and didnt really progress or confirm if it was right
 
  • #4
LowlyPion
Homework Helper
3,090
5
I know that torque = r x F or rFsintheta
i think it needs to use the ones related to angular momentum where torque= dL/dt= Id omega/ dt= I alpha
there was a similiar question but it just said the things and didnt really progress or confirm if it was right
OK. So you have

T = F * R = I * α

m*g*R = 1/2*M*R2 * α

but α = a/R

So ... m*g = 1/2*M*a
 

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