Homework Help: Kinematics Projective Motion Problem

physics7889 · Mar 23, 2010

Projectile Motion
1. The problem statement, all variables and given/known data
Joe Carter hit a fly ball during spring training. It just cleared a 10m fence, Calculate the speed of the ball when it leaves his bat at ground level. Ignore friction.
http://img155.imageshack.us/img155/7161/physics.png [Broken]

2. Relevant equations

3. The attempt at a solution
v in x direction was found to equal 12.5 m/s which is the same as v in y direction since the tangent formed was a 45-45-90 degree angle triangle.

nickjer · Mar 23, 2010

You need to show your work, along with relevant equations. Also, what is the 8 m? Is that the distance from the batter to the wall, or the distance from the landing spot to the wall?

physics7889 · Mar 23, 2010

its the distance from the fence to the landing point of the projectile

nickjer · Mar 23, 2010

Is the 45 degree angle given to you, or something you solved for?

physics7889 · Mar 24, 2010

It was given to me, this is really all the information that was given

nickjer · Mar 24, 2010

Well it looks like your attempt at the solution is right so far. But it is recommended you show your work, so it doesn't look like you just copied the answer from somewhere.

Also, what do you know about the velocity in the x-direction since the only acceleration is the gravitational acceleration in the y-direction.

rl.bhat · Mar 24, 2010

When the ball reaches the ground, vx remains the same.
vyf^2 = vyi^2 + 2*g*h.
vyi is the same as vx, which you have found. h is given. Find vyf.
Initial velocity v = sqrt(vyf^2 + vx^2)