# Horizontally Launched Projectiles

## Homework Statement

An airplane loaded with flame retardant travels horizontally at 200. km/h. The altimeter indicates that the plane is 180. m above the ground. The pilot wants to know how far in advance of the fire to release the retardant. Please assist her.
The answer was given, which is 336 meters

d=vit+1/2at^2

## The Attempt at a Solution

So I plugged in all the numbers, 180 for d, 0 for vi, -9.81 for a. I got to 180=4.905t^2, which turns to 36.69. Then, I squared it, and got about 6.8, which is nowhere close to the time I need, which is 1.68. Please help me!

Spinnor
Gold Member
This problem is similar to firing a bullet horizontally with velocity of 200m/s and an altitude of 180m and asking how far it will travel. In the equation you used the initial velocity in the vertical direction is zero but I think you substituted the initial horizontal velocity.

See horizontal projectile motion,

http://www.mrfizix.com/home/projectilemotion.htm [Broken]

and,

Good luck.

Last edited by a moderator:
By Vi, I meant ViY. I don't understand what I did wrong from the pages you sent me to. I know I'm doing something way wrong, I'm just not sure what

Spinnor
Gold Member
By Vi, I meant ViY. I don't understand what I did wrong from the pages you sent me to. I know I'm doing something way wrong, I'm just not sure what

OK, your time looks right, so the distance should be t*200m/s which is much larger then the "right" answer. One of the numbers in your first post are wrong?

Yeah probably, I found these problems online, so they may be a bit messed up

Check your units. The problem specifies the horizontal velocity to be 200 km/h, not 200 m/s.