Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

You are not logged in.

## #1 2006-03-07 22:46:17

4littlepiggiesmom
Member
Registered: 2006-01-09
Posts: 42

### Wor problem using the h=-16t^2 +vt + s

Fire works are shot upward with an intial velocity of 125 feet per second from a platform 3 feet from ground. how lonh does the rock take to hit the ground?

I've gotten
16t^2= 125 + s and get 31.25 seconds?? am I close???

Offline

## #2 2006-03-07 23:35:01

ganesh
Moderator
Registered: 2005-06-28
Posts: 21,812

### Re: Wor problem using the h=-16t^2 +vt + s

The relevant formulae
are
(1) v=u+at
(2) S = ut + ½at²
and (3) v²=u²+2aS
Where S=displacement, u=initial velocity, v=final velocity, t=time, a=acceleration.
When a projectile is fired upward, the gravitational force of earth tends to retard the motion of the projectile. The acceleration due to gravity,
g=9.8 m/s².
Since this acts against the upward motion, a has to be taken as negative.
Moreover, all the quantities should be converted to SI Units.
With these hints, please try to solve the problem.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Offline