Initial Velocity (Without time and acceleration)

[djtsmith007]

Homework Statement

You are standing at the top of a cliff that has a stair step configuration. There is a vertical drop of 7 m at your feet, then a horizontal shelf of 9 m, then another drop of 3 m to the bottom of the canyon, which has a horizontal floor. You kick a 0.26 kg rock, giving it an initial horizontal velocity that barely clears the shelf below.

What initial horizontal velocity v will be required to barely clear the edge of the shelf
below you? How far from the bottom of the second cliff with the rock land?

Homework Equations

d=Vi(t)+(1/2)(a)(t^2)

The Attempt at a Solution

Cant seem to get around the problem without knowing more.

 

[kuruman]

Can you find the time required for the rock to reach the point where it barely clears the edge of the shelf?

 

[djtsmith007]

Can you find the time required for the rock to reach the point where it barely clears the edge of the shelf?

I haven't been able to

 

[Anden]

You can find the time by using gravity and the fact that the first step is 7 meters down. How long does it take for the rock to fall 7 m? If you find it you can calculate how fast it must travel in a horizontal direction.

 

[djtsmith007]

You can find the time by using gravity and the fact that the first step is 7 meters down. How long does it take for the rock to fall 7 m? If you find it you can calculate how fast it must travel in a horizontal direction.

Could you help me out a little more?

 

[djtsmith007]

You can find the time by using gravity and the fact that the first step is 7 meters down. How long does it take for the rock to fall 7 m? If you find it you can calculate how fast it must travel in a horizontal direction.

So I am assuming you mean:
7m/9.8=.7142857s to make it to the bottom =t

using

d=(Vi+Vf/2)(t)
therefore
9m=(0+Vf/2)(.7142857s)
Vf=25.2

that not right?

 

[djtsmith007]

anyone?

 

[kuruman]

Use the equation that you initially quoted as "relevant" for the vertical motion. Identify ll the quantities - you know all of them except the time. Remember, vertical motion only.