What Did I Do Wrong in My Physics Homework Problem?

[shawonna23]

Physics Homework Problem--Stuck!

A diver springs upward with an initial speed of 1.7 m/s from a 3.0 m board.

a. Find the velocity with which he strikes the water. (Hint: When the diver reaches the water, his displacement is y = -3.0 m (measured from the board), assuming that the downward direction is chosen as the negative direction.)

b. What is the highest point he reaches above the water?


I tried using this equation, but my answer was wrong. Can someone tell me what I did wrong?

Part a:
d=v*t + 1/2 at^2
-3.0=1.7t + 1/2(-9.80)t^2
4.9t^2 - 1.7t -3.0=0
t= 0.98s

v=d/t
v=3/0.98
v=3.06m/s

I didn't do Part b because Part a was wrong!

 

[Gamma]

This question was asked before by you and was answered.

 

[Jameson]

He's going to travel up in the air, stop at the top, then come back down. This can be described by two equations, one going up and one going down.

For the first part:

$${V_f}^2 = {V_i}^2 + 2ad$$

You know the initial velocity, the final velocity (0), and the acceleration. Solve for the distance traveled.

For the second part you use the same equation, with 3 + part A as your total height. You know the rest of the numbers.