Number of Revolutions per minute and radians per second given diameter of wheels and speed A car is moving at a rate of 80km/hr. The diameter of its wheels is 60cm. 
(a) Find the number of revolutions per minute that the wheels are rotating.
(b) Find the angular speed of the wheels in radians per second.
I have performed the calculations and have:
(a) 707.36 revs/min
(b) 112.58 radians per second.
Would really appreciate it if someone could check these answers out for me, as we don't have memos. Thanks!
 A: The radius of the wheels are $r=30$cm$=0.3$m
Then the circumference is given by $C=2\pi\cdot r= 0.6\pi$metres
The car moves at $80$kmh$^{-1}=80,000$mh$^{-1}=\frac{4000}{3}$m min$^{-1}$
Then the revs per minute are given by $\frac{\frac{4000}{3}}{0.6\pi} = 707.355... \approx 707.36$revs/min - so your first answer is correct.
The car moves at $\frac{200}{9}$ms$^{-1}$
Note that $v=r\omega$, where $\omega$ is the angular velocity
So the angular speed of the wheels is given by $\frac{\frac{200}{9}}{0.6\pi}\cdot 2\pi =74.07...\approx 74.1$rad s$^{-1}$
So I believe your second answer is incorrect.
A: 80 km/h $\;≈22.22$ meters per second. 
The diameter is $\;0.6$ meter. The circumference is roughly $\;3.14\cdot 0.6≈1.88$ meters.
So we get $22.22/1.88≈11.8$ revolutions per second or $\,≈700$ RPM.
One revolution is $360^\circ$ or $2π≈6.28$ radians. 
 Here it is gonna be $\;11.8\cdot6.28≈74\;$ radians per second or angular velocity in seconds.
I saw the answer was already given to you but anyway, just in confirmation, since I've also typed it, I'm leaving it here too. 
