Basil L.

asked • 09/08/15

Kinematics (height and velocity)

A rocket travelling upward has a height above the ground given by x(t)=At2-Bt3, where A and B are positive constants.
In terms of A and B, what are is maximum height and velocity the rocket will reach?
Will I need to be calculating a second derivative to get the maximums here?

1 Expert Answer

By:

Megan L.

Could you please expand on how to find the maximum velocity? I have gotten the second derivative for the acceleration equation, but don't know where to go from there.
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09/02/16

Shirin Z.

tutor
ok I will do the velocity
 
V=dx/dt=2At-3Bt^2
now if dV/dt=0 that is a maximum
so 
dV/dt =2A-6bt=0    => t=A/3B
 
so maximum is 2A(A/3B)-3B(A/3B)^2=(A^2)/3B
 
do not look at the second derivative as acceleration. It is just a derivative that if it is equal to zero will give you the maximum of the curve (in this case Velocity).
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09/02/16

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