How Do You Calculate Dragster Deceleration Time and Distance?

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SUMMARY

The discussion focuses on calculating the deceleration time and distance of a dragster that accelerates at 8 m/s² for 4.6 seconds and then decelerates to a stop over 100 meters. The first part of the problem was solved using the equation x = 0 + 1/2at², yielding a track length of 84.64 meters. For the deceleration phase, participants emphasized the need for additional equations to relate initial speed, final speed, time, and acceleration, particularly since the initial speed is not zero during deceleration.

PREREQUISITES
  • Understanding of kinematic equations, specifically x = 0 + 1/2at²
  • Knowledge of initial and final velocity concepts in physics
  • Familiarity with acceleration and deceleration calculations
  • Ability to solve systems of equations with two unknowns
NEXT STEPS
  • Study the kinematic equations for motion with constant acceleration
  • Learn how to derive time and acceleration from initial and final velocities
  • Explore practical examples of dragster physics and performance calculations
  • Review problem-solving techniques for physics involving multiple variables
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Students studying physics, particularly those focusing on kinematics, as well as automotive engineers and enthusiasts interested in drag racing performance metrics.

Casey Wilson
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Homework Statement



- A Dragster at the starting line accelerates at 8 m/s^2 to the finish line. If it took 4.6 s, how long is the track?
- The Dragster deccelerated to a stop in 100m. How long did it take?

Homework Equations



x = 0 + 1/2at^2

The Attempt at a Solution



The first part of the questions I got x = 84.64m using the above equation.
For the life of me, I cannot figure out how to get anything viable for other formulas, when v or a is not specified for decceleration (read: Part 2).
 
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Hello casey, welcome to PF :)

Same formula, but now the initial speed isn't zero. And x isn't the unknown, because it's a given. The unknown is a. And t of course. So you'll need another equation. Something relating v initial, v final, t and a.

From there (with v final = 0) you'll find t. (two equations with two unknowns)

You'll do fine.
 
BvU said:
Hello casey, welcome to PF :)

Same formula, but now the initial speed isn't zero. And x isn't the unknown, because it's a given. The unknown is a. From there (with v final = 0) you'll find t. (two equations with two unknowns)

You'll do fine.

I think I see where you are coming from.
Thank you for the quick reply and the welcome.

I missed the second part of your answer. I think I got it figure out. Thank you!
 
Ah, some PF culture here: you do the work, helpers help. So jot something down and solicit comments/assistance !
You'll need this other equation anyway (it's no big deal, you must have seen it come by already at some point in the lectures/testbook) to determine the speed when the braking starts.

Hint: check out the formulas here (where it says three key variables)
 
Last edited:
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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