# Homework Help: Projectile Motion Water hose Question

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1. Oct 1, 2015

### jasonchiang97

1. The problem statement, all variables and given/known data
A water hose is used to fill a large cylindrical storage tank of diameter D and height 2D . The hose shoots the water at 45 ∘ above the horizontal from the same level as the base of the tank and is a distance 6D away

2. Relevant equations

Vx=Vt
D=vit+1/2at^2

3. The attempt at a solution
I tried plugging in the values into the equation and I end up with√6dG<V<√√7dG

2. Oct 1, 2015

### haruspex

You should not apply equations without understanding the context in which they are valid. The equation you tried does not allow you to use the height of the tank, so it cannot be appropriate. When is it appropriate?

3. Oct 1, 2015

### jasonchiang97

Right, okay I think I'm only allowed to use the equation when the object is landing at the same level ground as it started off on.

4. Oct 1, 2015

### haruspex

Right. Or, more precisely, when d is the distance to a point where it is at the same level it started at.

5. Oct 1, 2015

### Staff: Mentor

What is the question? What are you trying to find?

6. Oct 1, 2015

7. Oct 1, 2015

### jasonchiang97

oops. Sorry I thought I posted that.

8. Oct 1, 2015

### Staff: Mentor

Okay, so what are the scenarios for the water stream that you need to investigate? That is, what are the significant characteristics of the trajectory in each case?

9. Oct 1, 2015

### @navin

OK. From where is the hose 6D away? From the centre of the tank? Or from where the tank begins?

10. Oct 1, 2015

### Staff: Mentor

Clever student's strategy: Unless the problem states a condition explicitly, choose the simplest situation to work with and declare it as an assumption. Just make sure that it's really undefined and not subtly implied somehow in the problem statement.

11. Oct 1, 2015

### @navin

You can't use dg = v^2(sin∆) here as this is equation gives us the maximum range of the projectile.

12. Oct 1, 2015

### haruspex

See post #3.

13. Oct 1, 2015

### haruspex

So what equation should you use here?

14. Oct 1, 2015

### jasonchiang97

I used the 2D equations and plugged in t=Vx/Vcos45 into d=vtsin45+1/2at^2 and solved.

Thanks

15. Oct 1, 2015

### haruspex

16. Oct 1, 2015

yep