(adsbygoogle = window.adsbygoogle || []).push({}); [SOLVED] Motion in two dimensions question. At wit's end.

Hi, I'll try to keep this short. I have a Physics exam tomorrow and was doing some textbook questions and can't figure out this one problem. It's killing me! I have the answer (supplied by the back of the book), but just can't seem to get there.

Some help would be much appreciated since I've grown very frustrated with it.

1. The problem statement, all variables and given/known data

The initial speed of a projectile is 80 m/s. If the projectile is to strike a target that is a horizontal distance of 450 m away, what is the minimum time of flight. (Answer 6.1s)

2. Relevant equations

Standard laws of motion ignoring air resistance and the like

X(final) = X(initial) + V(initial) (t) + 0.5at^2

3. The attempt at a solution

I've tried everything I can think of. What's shutting me down every time is that there is no angle supplied so I'm always stuck with two variables I can't eliminate.

Obviously the answer must lie in finding the smallest angle possible for a projectile at 80 m/s to reach 450 meters, I just can't figure out how. I came up with this equation from the formula above, but I have no clue how to use it as my brain is just shutting down at this point (maybe it's useless i don't know, argh!)

450 = 0 +80(cos(alpha))t = 0

t= 5.625/cos(alpha)

If someone could help me get this problem you would earn my undying admiration, and I'll mail you a cookie!

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# Homework Help: Motion in two dimensions question. At wit's end.

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