Kinematics of rocket - calculate total hang time

AI Thread Summary
The discussion focuses on calculating the velocity at liftoff of an air rocket based on its total hang time of 7 seconds. It is noted that the rocket reaches maximum height at 3.5 seconds, where the final velocity is zero. The relevant equations of motion are considered, particularly the relationship between initial velocity, acceleration, and time. By applying the equation v_i = v_f + a*t, with gravitational acceleration set at -9.8 m/s², the initial velocity is calculated to be 34.3 m/s. This demonstrates the application of kinematic equations to determine rocket launch parameters.
physicsphreak123
Messages
3
Reaction score
0
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 ?
 
Physics news on Phys.org
v_ = v_i - a t

0 = v_i - 9.8 * 3.5

v_i = 34.3 m/s
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Determine when (m), and how long the rocket should fire.
Replies
2
Views
1K
Kinematics: Two engines, One Rocket, and Displacement.
Replies
11
Views
2K
Kinematics: find maximum height
Replies
2
Views
4K
Kinematic Equation Rearrangement
Replies
1
Views
3K
What is the ideal value of T for the rocket to reach 990 m altitude?
Replies
9
Views
25K
Calculating Total Flight Time for a Rocket: A Scientific Approach
Replies
4
Views
2K
How to calculate velocity of infinite-stage rocket?
Replies
2
Views
1K
Kinematics: Motion in One Direction: Car Chase
Replies
9
Views
3K
Find the initial velocity of a water rocket (mass changes)
Replies
8
Views
2K
Kinematic Equations Problem: Toy cars on adjacent tracks
Replies
2
Views
2K

Hot Threads

Recent Insights

Back
Top