My Math Forum  

Go Back   My Math Forum > Science Forums > Physics

Physics Physics Forum


Reply
 
LinkBack Thread Tools Display Modes
October 28th, 2009, 11:29 AM   #1
Member
 
Joined: Oct 2009

Posts: 39
Thanks: 0

Speed problem

I am not sure this problem belong to this section or not, but here it goes. I have been trying to solve this for a while.

A bicyclist makes a daily ride of 40 miles at a constant speed. If he trains hard, he can increase his speed by 4 miles per hour, which would result in a half-hour decrease in time. Find his new speed.

I tried many ways. One was to set up a table like this

V T D
--------------------------------------------
v t 40
---------------------------------------
v+4 t-.5 40

But we still have 2 variables to solve??? Are we suppose to guess for one of the variable????

Any help is appriciated. Thank you.
alikn is offline  
 
October 28th, 2009, 05:36 PM   #2
Global Moderator
 
Joined: May 2007

Posts: 6,378
Thanks: 542

Re: Speed problem

Quote:
Originally Posted by alikn
I am not sure this problem belong to this section or not, but here it goes. I have been trying to solve this for a while.

A bicyclist makes a daily ride of 40 miles at a constant speed. If he trains hard, he can increase his speed by 4 miles per hour, which would result in a half-hour decrease in time. Find his new speed.

I tried many ways. One was to set up a table like this

V T D
--------------------------------------------
v t 40
---------------------------------------
v+4 t-.5 40

But we still have 2 variables to solve??? Are we suppose to guess for one of the variable????


Any help is appriciated. Thank you.
You can set it up as 2 equations in 2 unknowns. Let v be the original speed and t the original time.

Start equation 40=vt
End equation 40=(v+4)(t-.5)=vt+4t-.5v-2. This leads to 4t-.5v=2.

Combine with first equation gives a quadratic in either t or v which can be solved.

This is an elementary algebra problem and should be in that section.
mathman is offline  
October 30th, 2009, 09:40 AM   #3
Member
 
Joined: Oct 2009

Posts: 39
Thanks: 0

Re: Speed problem

Thank you mathman. Do I need move this to elementary algebra section?
alikn is offline  
October 30th, 2009, 04:53 PM   #4
Global Moderator
 
Joined: May 2007

Posts: 6,378
Thanks: 542

Re: Speed problem

Quote:
Originally Posted by alikn
Thank you mathman. Do I need move this to elementary algebra section?
Leave that to the people running the forum.
mathman is offline  
Reply

  My Math Forum > Science Forums > Physics

Tags
problem, speed



Search tags for this page
Click on a term to search for related topics.
Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Find the ratio of his usual speed to his speed that day. Chikis Elementary Math 25 January 31st, 2014 09:48 AM
Speed Word Problem. ShaneR Elementary Math 2 December 28th, 2013 05:32 PM
Average speed problem haftakhan Algebra 1 August 11th, 2011 11:14 PM
Word speed problem alikn Elementary Math 3 December 15th, 2009 03:23 PM
A problem about speed and distance jkmartinez Calculus 0 October 27th, 2009 02:58 PM





Copyright © 2017 My Math Forum. All rights reserved.