# word problem

• Oct 10th 2008, 05:36 PM
robasc
word problem
A truck is moving at a rat of 90 kilometers per hour, and the diameter of its wheels is 1.25 meters. Find the angular speed of the wheels in radians per minute.

Here is what I got so far:

since I need meters I am going to convert kilometers to meters.

so... 90 kilometers * 1000 = 90,000 meters.

Next I need to figure out how many meters is in 60 minutes:

90,000/60 = 1500 meters in 60 minutes

Ok, now I need to find angular speed:

1500 * 2pi * .625 = 5980.49 radians per minute?
• Oct 10th 2008, 06:37 PM
ticbol
"90,000/60 = 1500 meters in 60 minutes"
You mean, 1500 m/min -----that is the tangential speed at the circumference of the wheel.

You know that
v = w*r
where
v = tangential speed
w = angular speed

So,
1500 = w(0.625)
• Oct 12th 2008, 05:02 PM
repcvt
I think should be 1500/(pi*1.25)
• Oct 18th 2008, 12:03 PM
HallsofIvy
Quote:

Originally Posted by robasc
A truck is moving at a rat of 90 kilometers per hour, and the diameter of its wheels is 1.25 meters. Find the angular speed of the wheels in radians per minute.

Here is what I got so far:

since I need meters I am going to convert kilometers to meters.

so... 90 kilometers * 1000 = 90,000 meters.

Next I need to figure out how many meters is in 60 minutes:

90,000/60 = 1500 meters in 60 minutes

No. 90000 m/h is 90000 meters in 60 minutes because 60 minutes IS an hour. What you have calculated is that the distance moved is 1500 m inone minute. Clearly that was what you meant because that is how you use it below.

Quote:

Ok, now I need to find angular speed: