Find the initial velocity of a projectile

[Workout]

Homework Statement

So it's based off of a track&field long jumper. Calculate the initial speed, v0, of a long-jumper where d=7.87 m. Assume a take-off angle of 21.4°, an initial height of the centre-of-mass of 0.920 m, and a final height of 0.460 m.

So I use the range equation for projectile motion and rearrange it for velocity but it doesn't seem to work...


can someone correct me?

Homework Equations

x = v^2/gsin2(theta) where x is the range. i rearranged for velocity.

The Attempt at a Solution

x = v^2/gsin2(theta)

v = sqrt(xgsin2(theta)
= sqrt(7.87m*9.8*sin(2*21.4)
= 7.24 m/s

 

[szynkasz]

Your equation works when initial and final height is the same. Here it isn't