# Parametrics/phyics question

If a rock is thrown from a point 3 ft above the ground with a horizontal velocity of 90ft/sec and a vertical velocity of 47 ft/sec, how far away will it land if nothing is obstructing its path? If there is a 7'9" fence in front of you, will the rock sail over the fence?

Actually, this is a problem in my calc book. I'm supposed to solve it using parametric equations but I figured its still physics...

Using parametrics: the
x(t)=x0+h0t
x(t)=90t

y(t)=(-1/2)gt2+v0t+yo
y(t)=-16t2+47t+3

Using physics:
Not sure which equation to use. I'm a little confused. I started by adding the velocity vectors, and got 101.5 ft/s in an upwards diagonal direction
I used v2=v02+2ax
v=0, v0=101.5, solved for x and got 525.625.
answer should be 270. no idea what to do.....

I'd prefer to work with the parametric method but any help is welcome....Thanks

## Answers and Replies

rl.bhat
Homework Helper
y(t)=-16t^2+47t+3
Since the rock lands on the ground, take y(t) = 0. Solve for t.

ah thanks. got it =)