How High Is the Diving Platform?

[Londoncalling]

Homework Statement

You jump off a diving board with a horizontal velocity of 1.81 and land in the water 1.4 seconds later. Gravity=9.8. How high is this platform?

Homework Equations

x=2.534, if that helps.

The Attempt at a Solution

I got 7.07 but this is not right...

 

[rl.bhat]

Hi Londoncalling, welcome to PF.
What is the velocity in the vertical direction? What is the kinematic equation, which relates the initial velocity, time , acceleration and displacement?

 

[Londoncalling]

y=v_it-.5gt² right?
I'm not sure though, we haven't learned it yet.

 

[rl.bhat]

In the vertical direction the initial velocity is ...?
Your equation is right. But put -y for the displacement because it is also in the downward direction like g.

 

[Londoncalling]

Okay so -y=v_i -.5*9.8*1.4².
Then -y=v_i*1.4-(4.9*1.96)
-y=v_i*1.4-(9.604)
But there are 2 variables and only one equation... I thought you couldn't do that...?

 

[Londoncalling]

Or is your horizontal v of 1.81 the initial velocity?

 

[rl.bhat]

The vertical velocity is zero.

 

[Londoncalling]

So it's 9.604 m high then?
Edit: Yes, I got it right! Thank you SO much, you have no idea how relieved I am. Would you be able to help me with another problem (it's in a different post)...?