Rocket Acceleration Calculation: Pendulum Swing During Liftoff Explained

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Homework Help Overview

The discussion revolves around a physics problem involving the behavior of a pendulum during a rocket's liftoff. The original poster describes observations of the pendulum's period changing from 2.46 seconds on the launch pad to 1.26 seconds during liftoff, prompting a question about the rocket's acceleration and the apparent increase in gravitational acceleration.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the use of the equation for the period of a pendulum and question how to apply it to find the rocket's acceleration. There is confusion about whether to calculate a new value for gravitational acceleration based on the pendulum's behavior during liftoff.

Discussion Status

Participants are actively engaging with the problem, sharing their calculations and questioning each other's methods. Some have provided guidance on how to approach the problem, while others express uncertainty about the correct equations to use for determining the rocket's acceleration.

Contextual Notes

There is mention of a hint provided in the problem statement regarding the increase in "g" within the rocket, which is a point of confusion for participants. Additionally, the original poster notes that hints have been disabled by the teacher, adding to the challenge of the discussion.

rr263
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Homework Statement


An astronaut notices that a pendulum which took 2.46 seconds for a complete cycle of swing when the rocket was waiting on the launch pad takes 1.26 seconds for the same cycle of swing during liftoff. What is the acceleration of the rocket?(Hint: Inside the rocket, it appears that g has increased.)


Homework Equations



T=(2pi)sqrt(L/g)

The Attempt at a Solution



I know I am supposed to use the above equation, but I don't know how to use it to solve for acceleration. Using g=9.8m/s^2 and the initial period, I solved for L and got 0.621m. Do I even need to do that for this problem? The fact that the problem said that "g" increased within the rocket is what confuses me the most. Am I solving for a new/increased value of "g" and using that as acceleration? If so, when I solved the problem this way, I got g=15.4 m/s^2 (using the second period and 0.621m as L), but this was incorrect.

I really need help with this problem as my teacher disabled the hints option. Thanks in advance.
 
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rr263 said:

Homework Statement


An astronaut notices that a pendulum which took 2.46 seconds for a complete cycle of swing when the rocket was waiting on the launch pad takes 1.26 seconds for the same cycle of swing during liftoff. What is the acceleration of the rocket?(Hint: Inside the rocket, it appears that g has increased.)


Homework Equations



T=(2pi)sqrt(L/g)

The Attempt at a Solution



I know I am supposed to use the above equation, but I don't know how to use it to solve for acceleration. Using g=9.8m/s^2 and the initial period, I solved for L and got 0.621m. Do I even need to do that for this problem? The fact that the problem said that "g" increased within the rocket is what confuses me the most. Am I solving for a new/increased value of "g" and using that as acceleration? If so, when I solved the problem this way, I got g=15.4 m/s^2 (using the second period and 0.621m as L), but this was incorrect.

I really need help with this problem as my teacher disabled the hints option. Thanks in advance.

How did you get 0.621? I got something different. Did you forget to square both sides of the equation at some point? There is a square root sign.
 
yeah you are right. i did do something qrong. i redid it and got 1.50
 
1.50 m is correct. What do you get for the new g value using 1.50 m and the shorter period?

Note: this new g value is not the acceleration of the rocket.
 
Thanks. Sorry it took so long to respond I have been at work all day. Anyways, with using 1.50m as the length and the shorter period of 1.26 seconds, I get a new value of "g" as 37.3 m/s^2
 
Sounds good. So, what must the rocket's acceleration be, to produce an apparent "g" of 37.3 m/s^2?
 
This is where I get stuck. I know that in order to accelerate, the rocket must overcome this new "g" value, but I don't know what equation I would use to figure out the rocket's acceleration.
 
Okay. Well, for example:

If the rocket were not accelerating at all, the apparent g would just be the usual 9.8 m/s^2.

If the rocket accelerates at 1.0 m/s^2, the apparent "g" becomes 10.8 m/s^2.

etc.
 
I got it! Thank you so much! Wow I didn't think it could have been that easy! Thanks again!
 

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