# projectile motion

Thread Starter

#### braddy

Joined Dec 29, 2004
83
Hi,

Please somebody help me with this problem:

A boy wants to knock down a coconut with a rock and his slingshot. He observes that the coconut is about 3.0m above his slingshot and the tree is 4.0m away along the ground.
He knows from experience that the release speed of his rock is 20m/s.
How far above the coconut should he aim?

Please can someone help me?

thank you

B.

#### haditya

Joined Jan 19, 2004
220
the equation of the projectile is given by
y = x.v.tan p - 0.5*g.x.x.(sec p)^2

put x=3,y=4 solve for p

the height above which to aim is given by 3*tanp

the 1st projectile equation is got by eliminating time t in the 2 equations given below
x=v*cos p * t
y=v*sin p * t -0.5g*t*t

Thread Starter

#### braddy

Joined Dec 29, 2004
83
Originally posted by haditya@Sep 17 2005, 09:16 AM
the equation of the projectile is given by
y = x.v.tan p - 0.5*g.x.x.(sec p)^2

put x=3,y=4 solve for p
[post=10403]Quoted post[/post]​
Thankx I will try this