Time for rocket shot upward to reach the ground

[helpmedude]

Homework Statement

A model rocket releases its first stage when it is 100.0 m above the ground and moving upward at 40.0 m/s. Ignoring air resistance, find:

the time it takes the first stage to hit the ground

Homework Equations

Y=Yo+VyoT+1/2GT^2

Quadratic

The Attempt at a Solution

I got to [-(40)+-Squareroot(1600-1960)]/9.8

the problem is that the square root of a negative number is an imaginary number so I am just wondering what I am missing here?

 

[alphysicist]

Hi helpmedude,

Homework Statement

A model rocket releases its first stage when it is 100.0 m above the ground and moving upward at 40.0 m/s. Ignoring air resistance, find:

the time it takes the first stage to hit the ground

Homework Equations

Y=Yo+VyoT+1/2GT^2

Quadratic

The Attempt at a Solution

I got to [-(40)+-Squareroot(1600-1960)]/9.8

I don't believe that is correct. What numbers did you use for Y, Y0, Vy0, and G?

 

[helpmedude]

my bad I forgot to make acceleration due to gravity negative that's why it didnt work geez. thanks anyways. Y=0 Yo=100m Vyo=40.0m/s G=-9.8m/s^2 I used 9.8m/s^2