# S.O.S. Mathematics CyberBoard

Your Resource for mathematics help on the web!
 It is currently Tue, 18 Jun 2013 08:18:39 UTC

 All times are UTC [ DST ]

 Page 1 of 1 [ 2 posts ]
 Print view Previous topic | Next topic
Author Message
 Post subject: physics - workPosted: Tue, 1 Jul 2003 02:38:56 UTC
 Senior Member

Joined: Sat, 7 Jun 2003 00:26:42 UTC
Posts: 52
A force of 10 lb is required to hold a spring stretch 4 in. beyond its natural length. How much work is done in stretching it from its natural length to 6 in. beyond its natural length?

The answer my book gives me is 15/4 ft-lb. Is there anyway to do this without converting to feet? The solution in my book converts everything to feet and then finds the answer. Is here any other way to solve this just with the info given?

I understand that you must use the formula
f(x) = kx (Hooke's Law)

Thanks.

Top

 Post subject: Posted: Tue, 1 Jul 2003 15:53:14 UTC
 Member of the 'S.O.S. Math' Hall of Fame

Joined: Sun, 22 Jun 2003 18:00:06 UTC
Posts: 3461
Location: North TX
You either have to use inches or feet, which requires a conversion.
It should not be a big problem, however, since 6 in = 1/2 ft and
4 in = 1/3 ft

determine the spring constant k...
F = kx
10 lbs = k*(1/3 ft)
30 lbs/ft = k

W = (1/2)k*x^2
W = (1/2)(30 lbs/ft)(1/2 ft)^2
W = 15/4 ft-lbs

If you wish to use inches...
F = kx
10 lbs = k(4 in)
(5/2) lbs/in = k

W = (1/2)k*x^2
W = (1/2)(5/2 lbs/in)(6 in)^2
W = 45 in-lbs
note that (45 in-lbs)(1 ft/12 in) = 45/12 ft-lbs = 15/4 ft-lbs

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 2 posts ]

 All times are UTC [ DST ]

#### Who is online

Users browsing this forum: No registered users

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forum

Search for:
 Jump to:  Select a forum ------------------ High School and College Mathematics    Algebra    Geometry and Trigonometry    Calculus    Matrix Algebra    Differential Equations    Probability and Statistics    Proposed Problems Applications    Physics, Chemistry, Engineering, etc.    Computer Science    Math for Business and Economics Advanced Mathematics    Foundations    Algebra and Number Theory    Analysis and Topology    Applied Mathematics    Other Topics in Advanced Mathematics Other Topics    Administrator Announcements    Comments and Suggestions for S.O.S. Math    Posting Math Formulas with LaTeX    Miscellaneous