Wheel slowing from 210 rpm to rest in 15 seconds

[Mowgli]

Homework Statement

A 26.0 in diameter wheel is rotation initially at 210.0 revolutions per minute. It slows down uniformly and comes to rest in 15.0 seconds.

a.) what is the angular acceleration?
b.) through how many revolutions did it turn in those 15.0s?

Homework Equations

The Attempt at a Solution

a.)

f= 210.0 / 60s = 3.5 Hz

ang. accel= 2(pi)f= 2(pi) x 3.5
= 21.99 rad/s

21.99 / 15.0 = 1.47 rad/s^2

b.) 1/2(210 + 0)(15.0)
= 1/2(3150)
= 1575
= 1.60 x 10^3 rev

Can anyone confirm?

 

[bp_psy]

Homework Statement

A 26.0 in diameter wheel is rotation initially at 210.0 revolutions per minute. It slows down uniformly and comes to rest in 15.0 seconds.

b.) 1/2(210 + 0)(15.0)
= 1/2(3150)
= 1575
= 1.60 x 10^3 rev

Can anyone confirm?

There is a problem here your wheel is slowing down but makes more revolutions in 15s then in a min at the initial velocity.What equation are you using there ?

 

[Mowgli]

for b.) i was using theta = 1/2(initial velocity + final velocity) x time

 

[bp_psy]

b.) 1/2(210 + 0)(15.0)
= 1/2(3150)
= 1575
= 1.60 x 10^3 rev

Check your units. You should not use t=15s. Your units must be consistent.

 

[Mowgli]

f= 210.0 / 60s = 3.5 Hz

so 1/2(3.5 + 0) (15)
= 1/2 (52.5)
= 26.25 rev

 

[bp_psy]

Now use another equation to check your answer.