Velocity Decay Curve for a Rocket

In summary, the conversation is about solving a problem involving the integral of a decay curve and finding the initial velocity of a rocket in order for it to travel a certain distance in a given time interval. The formula D=Ar(1-e-t/r) is used, with D, r, and t being known values and A being the unknown. The individual is stuck on how to calculate A but has been unable to find the answer after hours of searching. They suggest replacing a known value with a calculated one to solve for A.
  • #1
pete321
3
0
Homework Statement
suggest a new initial velocity A of the rocket
Relevant Equations
$$\large \int_0^{t_L} A e^{\frac{-t}{\tau}} \text{d}t = A \tau \left( 1- e^{\frac{-t}{\tau}} \right)$$
I am trying to solve the problem below. I have previously calculated from 0 to 4 seconds how far the rocket will travel in each second. I am stuck now as to how to start this problem. I have searched but unable to find the answer. Do i need to rearrange this? A is currently 14 which does not get the rocket to travel 15m in 4 seconds. Once i know how to start this i want to solve on my own so i understand how to complete this.

The integral of the decay curve of the form:
$$Ae^{\frac{-t}{\tau}}$$ This can be expressed as follows:

$$\large \int_0^{t_L} A e^{\frac{-t}{\tau}} \text{d}t = A \tau \left( 1- e^{\frac{-t}{\tau}} \right)$$

$$a = 14$$

$$\tau = 1.6$$

$$ t = 4$$Given this information, suggest a new initial velocity A of the rocket, which will allow the rocket to travel 15m in the same time interval of 0 to t=4.
 
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  • #2
Looks to me like you have an equation with 3 knowns (t, r, and distance) and 1 unknown (a). Can you solve for the 1 unknown?
 
  • #3
Thank you for your reply. No this is where i am confused. Is A now 15. As when t is 4 seconds the distance will be 15 not 14? I just don't understand how to calculate this. I have been searching for hours with no luck
 
  • #4
replacing 14 with 10.22 in the formula =15.0097. So would A be 10.22? If so just need to work out how to calculate it
 
  • #5
pete321 said:
replacing 14 with 10.22 in the formula =15.0097. So would A be 10.22? If so just need to work out how to calculate it
Like I said, you have 3 knowns and 1 unknown.
D=Ar(1-e-t/r), and we know D, r, and t.
So you rearrange the equation to solve for A.
 
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