BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Number of revolutions

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 447
Joined: Sun Apr 19, 2009 9:08 pm
Location: Kolkata,India
Thanked: 7 times
GMAT Score:670

Number of revolutions

by uptowngirl92 » Fri Oct 09, 2009 1:04 am
The radius of the front wheels of a cart is half that of the rear wheels. If the circumference of the front wheels is 1 meter and the cart traveled 1 kilometer, how many revolutions did the rear wheels make?
Top
Source: — Problem Solving |
User avatar
Community Manager
Posts: 1537
Joined: Mon Aug 10, 2009 6:10 pm
Thanked: 653 times
Followed by:252 members

by papgust » Fri Oct 09, 2009 1:08 am
Is the answer 500 revolutions?
Top
Master | Next Rank: 500 Posts
Posts: 182
Joined: Sun Aug 02, 2009 7:19 pm
Thanked: 18 times
GMAT Score:680

by sanjana » Fri Oct 09, 2009 1:33 am
Rear Wheels :
Radius : r
Front Wheels :
Radius : r/2

Circumfrence of Front wheels = 1m
Hence, 2*PI*r = 1m
==> 2*pi*r/2 = 1m
==> r=1/pi

Now Circumfrence of Rear wheel : 2*pi*r = 2*pi*1/pi
=2m

Now in 1 revolution(circumfrence) the rear wheel covers 2m
Therefore to cover,1000m(1km),No of rev = 1000/2=500.

Its got to be 500!
Top
Master | Next Rank: 500 Posts
Posts: 124
Joined: Thu Jun 18, 2009 5:33 am
Thanked: 35 times

by NikolayZ » Sat Oct 10, 2009 7:44 am
i think its 250/pi.
Assume that the front wheel has a radius X, ==> rear wheel has a radius 2X.
the circumference of the front wheel is 2*pi*x==> 2pi
The number of revolutions of the front wheel per one kilometer is 1000/2pi=500/pi.

Since the circumference of the rear wheel is twice the length of the front (hence 2*pi*2x=4pi) hence the number of revolutions for the rear wheel must be (500/pi)/2=250/pi
Top
Master | Next Rank: 500 Posts
Posts: 182
Joined: Sun Aug 02, 2009 7:19 pm
Thanked: 18 times
GMAT Score:680

by sanjana » Sun Oct 11, 2009 3:26 am
uptowgirl92,whats the OA?
Top
Post new topic Post Reply
• Page 1 of 1