- #1

- 6

- 0

## Homework Statement

How much time does it take from the rocket gets shot up, till it reaches the ground again?

The rocket accelerates 30m/s^2 for the first 3 seconds, and accelerates downwards -6m/s^2 after.

## Homework Equations

(v-v0) / a = t to find time

## The Attempt at a Solution

2ad=v^2-v0^2

d= time

v=speed before landing

v0= starting speed 45m/s

I found v0 to be 45, (810/18)

810m the highest it gets, after 18 seconds.

i find v0^2 to be 2025

the distance must be 810 times 2? so 1620meter

I know the acceleration is -6 but ill just write 6 here for now

2*(6)*1620= 19440

2025+19440=21465

so v^2=21465

v=146

i go back to v=v0+at

(v-v0) / a = t

(146 - 45) / 6 = 16

the answer is supposed to be 34sec, and I am confused:)

my guess is i do something wrong with v or v0, i take v0 as the starting point (at 18 sec)