# [SOLVED] Need help with pulley problem

• Apr 22nd 2010, 08:21 PM
ogglock
[SOLVED] Need help with pulley problem
Hi, i need help with the following question:

The sprocket assembly for a
0.800 m diameter bike wheel is
shown here. If the rider can
pedal at 50.0 rotations per
minute, what speed will the bike
be traveling? Express your
the back sprocket is 0.050 m
and the radius of the front
sprocket is 0.150 m.

Here is the picture for reference:
[html]http://img191.imageshack.us/i/33012387.png/[/html]I don't know how to start this question, but i do know that the velocity of the pulley or sprocket is the same.
• Apr 22nd 2010, 09:39 PM
sa-ri-ga-ma
If the pedal is attached to the larges sprocket, and the wheel to the smaller sprocket, one rotation of pedal of 0,150 m radius will produce 3 rotations of smaller sprocket of radius 0.05 m.So the wheel will also rotate 3 rotations during one rotation of pedal.
Now proceed to find the speed of the bike.
• Apr 22nd 2010, 09:46 PM
ogglock
i understand how you got the three rotations but im stuck after that. The answer is suppose to be 22.6 but i can't even get close to it
• Apr 22nd 2010, 10:03 PM
sa-ri-ga-ma
Quote:

Originally Posted by ogglock
i understand how you got the three rotations but im stuck after that. The answer is suppose to be 22.6 but i can't even get close to it

In one rotation wheel travels π*D m,where D is the diameter of the wheel. In three rotation it will be moving 3π*D m.
In one minute pedal rotates 50 revolutions.
In one minute wheel rotates .........revolutions.
In one minute wheel travel ........... m.
In one hour wheel travel ........... m = ........km.
• Apr 22nd 2010, 10:07 PM
ogglock
Quote:

Originally Posted by sa-ri-ga-ma
In one rotation wheel travels π*D m,where D is the diameter of the wheel. In three rotation it will be moving 3π*D m.
In one minute pedal rotates 50 revolutions.
In one minute wheel rotates .........revolutions.
In one minute wheel travel ........... m.
In one hour wheel travel ........... m = ........km.

sorry but could you explain what the symbols π and m stand for
• Apr 22nd 2010, 10:10 PM
sa-ri-ga-ma
Quote:

Originally Posted by ogglock
sorry but could you explain what the symbols π and m stand for

π is pi ......3.1416... m is meter.
• Apr 23rd 2010, 01:25 PM
ogglock
sorry to ask again but can you show me how you did it.
• Apr 23rd 2010, 04:34 PM
bjhopper
Quote:

Originally Posted by ogglock
sorry to ask again but can you show me how you did it.

Hi oddlock,
You sure are having trouble here.
pedal rotates 50 revs per min. or 3000 revs per hr
rear sprocket rotates 3x3000 =9000 revs per hr= bike wheel revs per hr
distance traveled in one hr =9000xpi x wheel dia =22,619 m perhr or 22.62 km per hr

bjh
• Apr 23rd 2010, 04:40 PM
ogglock
thanks i was able to get it