# Projectile Motion Problem Help

1. Sep 24, 2012

### gabbiem10

I am in an Honors Physics I class at my school and we are just starting to learn about projectile motion. I am having a bit of trouble with some homework and am in need of help.

Problems:
1. I kick a rock horizontally off a ledge that is 20 m high. Once in the air, the rock is in free-fall. How far forward does the rock travel before hitting the ground?
A: I used ΔY=1/2(a)(Δt)^2 to solve for Δt if ΔY = 20m Vy,i = 0 m/s and
a = -9.8 m/s2. I got Δt ≈ 2.0s. Is it even possible to solve this with the given information?

2. A long-jumper leaves the ground with an initial velocity of 12 m/s at an angle of 28 degrees above the horizontal. Determine the long-jumper's time of flight.
I solved for the y component using Vy,i = Rsinθ and
Vx = Rcosθ. Vy,i = 5.6 m/s and Vx = 10.6 m/s. a = -9.8 m/s^2 but that was as far as I could get with the given information.

2. Sep 24, 2012

### azizlwl

1. Just a nudge, it won't go far forward. Forward depends on initial horizontal velocity.
2. Hidden data. Vertical displacement =0

3. Sep 24, 2012

### gabbiem10

The problem is that the initial horizontal velocity is not given neither is the horizontal displacement. The time was calulated base upon other given factors.