Angular speed and rotation of a tire at 100 km/hr

[trigger352]

Can someone get me started? This is a homework question that I just can't get started on.

No wonder it's a "challenge" question.

A car is traveling at 100km/hr.

A) What is the angular speed of a tire which has a radius of 36cm.

B) Through how many radians will the tire turn in 30s at this speed?

 

[whozum]

100km/hr = 360m/s

In one second, it travels 360m. Think of the distance along the tire rim travelled.
Can you find how many revolutions it completes in one second? (360m).

 

[ek]

100km/hr = 360m/s

In one second, it travels 360m.

UGH.

 

[whozum]

Did I butcher it?

100km/hr * 1hr/3600s * 1000m/1km = 27.77m/s

Yes I did. Sorry.

 

[trigger352]

Wouldn't I need to divide the circumfrence by the speed?

2pi(36)=2.26m

so, 360/2.26 = 159.2920 rotations/sec. That's wrong.

Because then 2pi, for one whole rotation would be
318.5841pi/1sec = 1000.86 radians/sec


Yeah, ok. What's wrong. =P

Edit: I redit the question the same way except I substituted 27.77 for 360. I got 38.something. Which isn't right either.

 

[whozum]

27.77m/s

2.26m/rev

27.77/2.26 = xxx rev/s

Its going to be about 12-13

 

[trigger352]

yeha, sorry - I got that much. The 38 was from the calculation to get ther radians/sec

12.2876pi/sec = 38.6027 ... Yeah I don't know what I'm doing there.

 

[whozum]

27.77m/s * 1rev/2.26m = 12.28rev/s
1 revolution = 2pi radians

12.28 rev = 75.4 radians

12.28rev/s = 75.4rad/sec

God now your confusing me. I'm going to bed, lol.