Motion dropping a stone: Time question

[Jeff97]

Homework Statement

A boy watches a leaf move down the stream at 0.30ms^1. He wants to drop a stone onto the leaf. Determine the position of the leaf at the instant when he must drop the stone.

Relevant Equations

I'll put one here once I know what one to use.

what I know d=35.75 t=? what am I meant to do with this problem? I'll add more to this area once I know some more. thanks. Is the leafs velocity considered inital? if so I know Vi

 

[haruspex]

I know d=35.75

What distance is this and how do you know its value?
Suppose he drops the stone when the leaf is underneath. What will happen?

 

[Jeff97]

@haruspex. I got the distance from the other problem, should I not be using it? If he drops the stone when the stones underneath him it will be past him once the stone reaches the leaf?

 

[haruspex]

I got the distance from the other problem, should I not be using it?

They sounded like completely different problems to me, but since I cannot see both in context I may be missing something. You do need to know the height from which the stone is being dropped.

If he drops the stone when the stones underneath him it will be past him once the stone reaches the leaf?

Right, but assuming you know the height (call it d) by how much will he miss the leaf?

 

[Jeff97]

I suppose I need a formula? that contains d, Vi? t?

 

[haruspex]

I suppose I need a formula? that contains d, Vi? t?

Yes, and one more (known).

 

[haruspex]

Vf? If so could you use d=Vi+Vf/2 t?

No, I wrote "known" (as an edit). You do not know Vf.

 

[Jeff97]

acceleration?

 

[PeroK]

I suppose I need a formula? that contains d, Vi? t?

Perhaps you could forget formulas for a moment. Suppose this was a real task. You really have to hit something moving along a stream by dropping a stone on it. Imagine that you get lots of chances. Each time you miss, someone releases another leaf and gives you another stone. Let's assume you have a watch. How do you achieve the task?

 

[haruspex]

acceleration?

Yes.

 

[Jeff97]

Ok, so what we know is that he must drop the stone so that it will land on the leaf 2.7 seconds later. If the water is running at 0.3 m/s, then we can find the distance from the bridge to the leaf position (horizontal):

d=vt =0.3 x 2.7 = 0.81 m, so he must drop the stone when the leaf is 0.81 metres before the bridge.

The speed of the stone when it hits the water is not needed in the question. And I use the time from the first question.

 

[haruspex]

Ok, so what we know is that he must drop the stone so that it will land on the leaf 2.7 seconds later. If the water is running at 0.3 m/s, then we can find the distance from the bridge to the leaf position (horizontal):

d=vt =0.3 x 2.7 = 0.81 m, so he must drop the stone when the leaf is 0.81 metres before the bridge.

The speed of the stone when it hits the water is not needed in the question. And I use the time from the first question.

That's all good, except that I am still not convinced the two questions are connected.
You refer to a bridge. There was no mention of such in post #1. Are you sure there's nothing else you've left out?