# If problem states acceleration is constant what is the acceleration?

survivorboiii
If problem states "acceleration is constant" what is the acceleration?

While gliding down a steep hill, a bike rider experiences constant acceleration. After 4.50 seconds, he reaches a final velocity of 7.50 m/sec. The bike's displacement was 19.0 meters.

I know that I'm supposed to be using one of the kinematics equations. But what do I put as acceleration when it says constant acceleration? What does variable a equal to?

t=4.5
vf=7.5 m/s
d= 19m
Find vi

## Answers and Replies

Staff Emeritus
Homework Helper
You've got time, the final velocity, and the total displacement. What equation, which includes acceleration and initial velocity, would you use which contains all of these quantities?

If you write down this kinematic equation and start plugging in what you know, you should be able to determine what 'a' is.

Hint: This is why you study algebra in school.

survivorboiii
There are two of them that includes all three given variables, but they also include acceleration and initial velocity, which I don't have. How do I solve for two unknown variables?

survivorboiii
I just had the idea that the initial velocity would be 0 m/s

djh101
You have two equations and two unknowns. In algebra, this is where you would be using substitution or elimination, although there's actually an easier way to do this problem since one of the kinematic equations already contains only one of your unknowns.

Edit: I guess you actually only have one unknown, since you aren't required to find acceleration.