Physics Homework Help; Torque?

Question

A softball player swings a bat, accelerating it from rest to 4.0 rev/s in a time of 0.40 s. Approximate the bat as a 2.2 kg uniform rod of length 0.95 m, and compute the torque the player applies to one end of it.

I can't seem to get it right

w= 2piF or 8pi = 25.12 rad

I = 2.2*.95^2 = 1.99

AngularAccel = W/T or 25.14/.4 = 62.8

1.99*62.8 = 125 M*N

What am I doing wrong?

Answer 1

First, keep track of everything you have:

Wo=0rev/s which is 0rad/s

Wf=4 rev/s which is 25.13rad/s

t=4s

m=2.2kg

L=.95m

Second, you are looking for torque, so you need to know the equation:

T=Ia

You can find "a" with rotational kinematics:

Wf=Wo + at

25rad/s= 0rad/s +4a

a=6.28 rad/s^2

You can find "I." The "I" for a long thin rod is 1/3mL^2.

1/3(2.2kg)(.95)^2=.66183.

Now, go back to the equation for torque and plug in "a" and "I."

T= .66183x6.28

T= 4.16

And don't forget the units!