# Maximum range of a projectile when launched at 45°(Physics by example, Rees, pr. 14)

by bentley4
Tags: physics by example, projectile
 P: 66 In this solution the t in the y-coordinate equation is substituted using the x-coordinate equation and ultimately leads to the answer. My questions: 1. Why don't I get the same answer when I substitute the v or v and t instead? 2. How am I supposed to know to substitute t in this example and not v? Attached Thumbnails
 HW Helper PF Gold P: 3,394 I don't see how you can get it by keeping the t. You don't know t, so how can you tell the maximum value of x that way? I get x = gtē/(2*tanΘ) and can't tell what combination of t and Θ provide the maximum x. It would be good to see your calc. There is no need to eliminate the v; it is a constant. But you must eliminate the variable t.
 P: 25 Well, the problem is quite easy to approach. Range is given by u^2 sin(2a) / g, where a is the projection angle. Since -1
P: 66

## Maximum range of a projectile when launched at 45°(Physics by example, Rees, pr. 14)

 Quote by Delphi51 I don't see how you can get it by keeping the t. You don't know t, so how can you tell the maximum value of x that way? I get x = gtē/(2*tanΘ) and can't tell what combination of t and Θ provide the maximum x. It would be good to see your calc. There is no need to eliminate the v; it is a constant. But you must eliminate the variable t.
Ok, now I understand. Thnx!

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