Kinematics of rocket - calculate total hang time

[physicsphreak123]

For a class expierement we went outside and watched an air rocket launch into the air, and measured the total hang time.

Only knowing the time, find the velcotiy at liftoff.

the time is 7 seconds, and i understand that at the maximun height the time is 3.5 seconds. I don't know which equation to use becuase i am not familar with knowing only one variable.

we have 4 equations to choos from.
D = v*t
Vf = Vi + a*t
D = Vi*t + 1/2 a * t
Vf squared = Vi squared +2*a*d

Can you help me ?

 

[mathmike]

v_ = v_i - a t

0 = v_i - 9.8 * 3.5

v_i = 34.3 m/s

 

[quicknote]

Based on the information provided, it seems like you are trying to calculate the initial velocity (Vi) of the rocket at liftoff. To do this, you can use the equation Vf = Vi + a*t, where Vf is the final velocity (which is 0 at the maximum height) and a is the acceleration due to gravity (which is a constant value of -9.8 m/s^2).

So, using the given values of Vf = 0, t = 7 seconds, and a = -9.8 m/s^2, we can rearrange the equation to solve for Vi:

Vi = Vf - a*t
Vi = 0 - (-9.8 m/s^2 * 7 seconds)
Vi = 68.6 m/s

Therefore, the initial velocity of the rocket at liftoff is 68.6 m/s. Keep in mind that this is assuming that the rocket was launched vertically and there were no external forces acting on it.

I hope this helps and good luck with your experiment! Remember, science is all about experimenting and learning from the results, so even if your calculations may not be perfect, it's important to keep exploring and asking questions.