# Homework Help: Trouble calculating the acceleration

1. Sep 19, 2008

### ERAUin08

Hey everyone I need some help with a problem. I am having trouble calculating the acceleration since I dont the the initial velocity.

1. The problem statement, all variables and given/known data
You are driving on the highway when you come across a speedometer test where the distances are maked on signs. When you pass the 0 mile marker, rather than holding your speed constant you press on the accelarator and hold it constant. You pass the 0.1 mile marker 16 s later, and the 0.2 mile marker 8 seconds after the 0.1 marker. a) What did you speedometer read at the 0.2 mile? b) what was your acceleration?

2. Relevant equations
d=v/t
d=0.2 miles=322m
time=24 s
3. The attempt at a solution
a) 322m=v/24s
V=13m/s
b) For the acceleration I am not sure.

2. Sep 19, 2008

### Dick

Re: Acceleration

If it's accelerating you CAN'T use v=d/t (and you can't use d=v/t anywhere. It's wrong). You have to use d=v0*t+(1/2)*a*t^2 where v0 is the initial velocity and a is the acceleration. Now if you put in the two given time points, you have two equations in the two unknowns v0 and a. Solve for them.