Posted by **Anonymous** on Friday, December 7, 2012 at 6:08pm.

You shoot a rocket straight into the air from the ground.It takes 8.0 seconds to come back down to the ground.What was its initial velocity ?

Vf^2=Vi^2+2ax

0=vi^2+2(-9.8)(8.0) <----- My work

vi^2=-156.8

I don't how to solve the last step

- Physics -
**drwls**, Friday, December 7, 2012 at 6:48pm
You could solve it by taking the square root of both sides of the equation. However, your equation is wrong. You are apparently trying to apply energy conservation at the top of the trajectory, where Vf = 0. In that case, the "x" term is not 8.0 (seconds). It should be the height of the trajectory, in meters.

The rocket spends 4.0 of the 8.0 seconds going up. Decelerating at a rate g, we have

g*t = Vf = 9.8*4 = 39.2 m/s

## Answer this Question

## Related Questions

- Physics - You shoot a rock with a wrist-rocket straight up, it takes 6 seconds ...
- physics - A rocket is fired straight up and accelerates upward at 24 m/s2 for 12...
- math - a model rocket is projected straight upward from the ground level. It is ...
- Math Gr 12 - A model rocket is shot straight into the air. Its height in meters ...
- PHYSICS - Ms. Anderson shoots an arrow straight up into the air. The arrow ...
- Physics! - Ms. Anderson shoots an arrow straight up into the air. The arrow ...
- Physics - Mr. Anderson shoots an arrow straight up into the air. The arrow ...
- physics - a rocket is launched from atop a 105-foot cliff with an initial ...
- Math - A rocket is launched upward and then falls to the ground. The height of ...
- algebra Please help - .A toy rocket is shot vertically into the air from a ...

More Related Questions