(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Your alpine rescue team is using a slingshot to send an emergency medical packet to climbers stranded on a ledge on the side of a mountain. If the height of the ledge is 270m (y = 270m) and the ledge is 390m from the slingshot (x = 390m), what is the initial velocity of the slingshot if the launch angle is 70 degrees?

V(o) = ?

x = 390m

y = 270m

Theta = 70 degrees

a(y) = -9.81

a(x) = 0

2. Relevant equations

Since the only acceleration is constant, I know that I must solve this problem using these equations:

V = V(0) + at

X = X(0) + V(0)t + 1/2at^2

V^2 = V(0)^2 + 2ax

3. The attempt at a solution

When I first attempted the problem, I figured I would have to solve for variables using the y-axis.

I used a variation of the third equation:

V(y)^2 = V(0)(y) + 2ay

And solved for V(0)(y). (V(y) is 0 when it hits the ledge):

0 = V(0)(y) + 2(9.81)(270)

I got:

72.78 = V(0)(y)

and then I plugged it into:

sin(70) = V(0)(y) / V(0)

V(0) = V(0)(y) / sin(70)

V(0) = 77.45 m/s

This was the only valid approach I could think of, but the online HW program I'm using says that this is the incorrect answer. I'm sure that this is very simple and I am just ignorant of something, but can anyone provide any pointers to help me out?

Thanks!

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# Projectile Motion: Find Launch Speed

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