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March 30, 2015

March 30, 2015

Posted by **Josh** on Saturday, January 11, 2014 at 6:44pm.

(a) What is the magnitude τ of the torque required to bring the smaller sphere from rest to an angular speed of 300 rad/s in 15 s?

N·m

(b) What is the magnitude F of the force that must be applied tangentially at the sphere's equator to provide that torque?

N

(c) What is the corresponding value of τ for the larger sphere?

N·m

(d) What is the corresponding value of F for the larger sphere?

N

- Physics -
**Damon**, Saturday, January 11, 2014 at 7:17pmI sphere = (2/5) mR^2

see http://hyperphysics.phy-astr.gsu.edu/hbase/isph.html

I1 = (2/5)3 (.25)^2 = .075

alpha = 300/15 = 20 radians/second^2

Torque = I alpha = .075*20 = 1.5 Nm

F1 = torque/R = 1.5/.25 = 6 N

now big sphere

I2 = (2/5)3 (.8)^2 = .768

torque = I alpha = .768*20 = 15.36 Nm

F2 = 15.36/.8 = 19.2 N

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