Homework Help: What is the acceleration of the sled?

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1. Nov 26, 2014

won der

1. The problem statement, all variables and given/known data
A sled starts from rest at the top of a hill and slides down without constant acceleration. At same later time, it is 80 ft. from the top ; 2s after that it is 125 ft. from the top ; another 2s it is 180ft from the top.

a.) What is the acceleration of the sled?
b.) how long did it take to go from the top to the 80ft point?

The attempt at a solution
I
I solved for the a of the 2nd point
125ft=a(2s+4s)^2/2
125ft = a(6s)^2/2
125ft = a36s^2/2
125ft = a18s^2/2
125ft= a9s^2
13.8889ft/s^2 = a

2. Nov 26, 2014

Joffan

I'm assuming "without constant acceleration" is actually "with constant acceleration".

I don't understand your working but it doesn't get you close to the real answer.

If you initially take the 80ft point as zero distance, zero seconds (s=0, t=0), you then have 2 equations you can fill in for s=ut+½at2

3. Nov 26, 2014

Staff: Mentor

Hi won der. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

Can you explain how you got the equation I marked **
Looks like a mistake on line I marked ***

Are you sure you meant to write "without" constant acceleration?

Last edited by a moderator: May 7, 2017