# Homework Help: Projectile Motion: Hitting a box with a softball

1. Oct 7, 2009

### indietro

1. The problem statement, all variables and given/known data
Students at an engineering contest use a compressed-air cannon to shoot a softball at a box being hoisted straight up at 10m/s by a crane. The cannon, tilted upward at a 30 degree angle, is 100m from the box and fires by remote control the instant the box leaves the ground. Students can control the launch speed of the softball by setting the air pressure. What launch speed should the students use to hit the box?
2. Relevant equations
3. The attempt at a solution
** This is an example from Physics for scientists and engineers - Knight and I dont understand how they got their position equation for the box.
So basically they say that you need to equate the vertical positions of the softball and the box at the instant that the ball has traveled 100m. so they then say:
(y1)s = (y1)b
((Voy)s)t - 1/2gt$$^{2}$$ = ((Voy)b)t
** so I dont understand why gravity would not act on the box as well? or are they just saying that since its moving at a constant speed, acceleration = 0 (so no gravity)..??

Last edited: Oct 7, 2009
2. Oct 7, 2009

### semc

Yeap you are right constant speed therefore acceleration is 0. No so long you are on the surface of Earth you will experience gravitational force unless say you are mageneto. The question stated that the box is moving at constant speed so the distance travelled would just be vt

Last edited: Oct 7, 2009
3. Oct 7, 2009

### indietro

thanks for clarification :)