Simple? Motion Equation Problems

[harujina]

Homework Statement

1. A soccer player with an initial velocity of 0 (rest position) accelerates uniformly as she runs down the field traveling 17m [E] in 3.8s. What is her final velocity?

2. A skier sits at rest on top of a hill. If the skier travels 70m [down] in 5.3s while accelerating uniformly, what acceleration does he experience?

Homework Equations

a = (vf-vi)/t ?

The Attempt at a Solution

So I used the above equation to try and solve these but they're not working?
The answer to 1 is supposed to be 8.9m/s[E] and the answer to 2 is 5.0m/s2 [down].

 

[voko]

You are not given the final velocity in this problem. Obviously, the equation you listed as relevant is not applicable. You need another equation. Examine carefully what is given in the problem and find an appropriate equation.

 

[harujina]

yes, but if i isolate vf and i get vf = vi +at, shouldn't that be ok to use?

 

[voko]

Acceleration is not given either.

 

[harujina]

oh; d= (vf+vi)/2t
okay i got it, thank you :)