Help please?!?

Question

A ball player hits a home run, and the baseball just clears a wall 20.0 m high located 117.0 m from home plate. The ball is hit an an angle of 35° to the horizontal, and air resistance is negligible. Assume the ball is hit at a height of 1.0 m above the ground.
(a) What is the initial speed?

(b) How much time does it take for the ball to reach the wall?

(c) Find the components of the velocity and the speed of the ball when it reaches the wall.
vy,f =
m/s
vx,f =
m/s
vf =
m/s

Answer 1

Hi Cheyenne,

 

If you start with the x(t) an y(t) equations for a projectile 

 

y(t)=y0+v0y*t-1/2gt²

x(t)=x0+v0x*t             where v0y=vsin(35) and v0x=vcos(35) are the y and x components of the initial velocity.

 

The task is to find v (the initial speed) to do this we can eliminate t by solving the x equation for t and substituting in the y equation.

 

This gives, after some algebra, y=tan(35)*x-g*x²/(2v²*cos²(35))

Now if you let x=117m, y=20m and x0=0, y0=1m you can solve this equation for v, I got v=39.89m/sec

 

So v0y=vsin(35)=22.88m/sec

     v0x=vcos(35)=32.68 m/sec

 

Check my arithmetic

 

Regards

Jim