# Math Help - Projectile Problems ?

1. ## Projectile Problems ?

A boy is at the window of his flat and throws a ball to his friend 24 m below. The ball is thrown with speed 10ms at an angle elevation alpha where tan alpha=5/12
i) If the friend is standing 8m from the wall of the flat, will he be able to catch the ball without moving ?

2. Originally Posted by moesizlak
A boy is at the window of his flat and throws a ball to his friend 24 m below. The ball is thrown with speed 10ms at an angle elevation alpha where tan alpha=5/12
i) If the friend is standing 8m from the wall of the flat, will he be able to catch the ball without moving ?
My suggestion is to find out where the ball will land on the ground. If it hits the ground at x = 8 m, then the ball can be caught.

So, I am setting an origin at the base of the building, with +x to the right and +y upward. The ball is being thrown at an angle above the +x axis.

Let's settle the question of the angle first. We can always find $tan^{-1}( 5/12)$ or we can simply note that $sin( \alpha ) = 5/13$ and $cos( \alpha ) = 12/13$.

Table of x "information"
x0 = 0 m
v0x = 10*cos(alpha)
x = ? (This is what we are looking for)
vx = v0x = 10*cos(alpha)
ax = 0 m/s^2

Table of y "information"
y0 = 24 m
v0y = 10*sin(alpha)
v = 0 m
vy = ?
ay = -g = -9.8 m/s^2

The time, t, it takes for the ball to hit the ground is unknown.

My suggestion is to find t from the y information, then use that value of t to find x.

Can you finish it from here?

-Dan