Solving Claire's Physics Problem: Minimum Angle to Outrun an Arrow

[gemini2904]

Homework Statement

Hi, From a previous question I have just worked out that the speed of the arrow launch is 20ms-1. The speed the mans can run is 7.0ms-1. Question, find the minimum angle above the horizontal at which the man must aim in order to outun the arrow. (you may assume the man is at rest when he fires the arrow and you may ignore the short times it takes him to accelerate from rest to his running speed).

Please help, I have been looking at this question for about a week now and I can't see for the life of me how you can possibly work this out without knowing the distance or anything else? I would be grateful if someone could please at least point me in the right direction. I'm doing a modular degree, 2nd year but this is my first physics course...ahhhhhh So please explain in detail, my maths is somewhat limited. I think I should have stuck to biology!


Many thanks,

Claire

Homework Equations

The Attempt at a Solution

 

[tiny-tim]

Welcome to PF!

From a previous question I have just worked out that the speed of the arrow launch is 20ms-1. The speed the mans can run is 7.0ms-1. Question, find the minimum angle above the horizontal at which the man must aim in order to outun the arrow. (you may assume the man is at rest when he fires the arrow and you may ignore the short times it takes him to accelerate from rest to his running speed).

Hi Claire! Welcome to PF!

Hint: you only need the horizontal component of the velocities.

So how does the arrow's horizontal component change over time?

(in other words: what's the equation for the horizontal component?)

 

[gemini2904]

Hi, Thanks very much for replying.

Do you mean Vox = Vo cos theta

cos theta = 7/20 = 0.35 so theta = 69.5


Many thanks,
Claire

 

[flatmaster]

Not only that, but if he shoots at exactly at that angle and keeps runing, he shoots himself in the back!1