Solving Deceleration Problem: Speed & Time Calculation

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SUMMARY

The discussion focuses on solving a deceleration problem involving a pickup truck that initially travels at 100 km/h and experiences a uniform deceleration of 6.5 m/s² over a distance of 20.0 m. The final speed of the truck is calculated to be 81.4 km/h, and the time elapsed during this deceleration is determined to be 0.794 seconds. Participants emphasize the importance of unit conversion and showing work to identify errors in calculations.

PREREQUISITES
  • Understanding of kinematic equations, specifically u² = v² + 2as and v = u + at
  • Familiarity with unit conversions between kilometers per hour (km/h) and meters per second (m/s)
  • Basic knowledge of acceleration and deceleration concepts
  • Ability to manipulate algebraic equations to isolate variables
NEXT STEPS
  • Learn how to convert between km/h and m/s accurately
  • Study the application of kinematic equations in various motion problems
  • Explore examples of uniform acceleration and deceleration scenarios
  • Practice solving real-world problems involving speed, time, and distance
USEFUL FOR

Students studying physics, particularly those focusing on kinematics, as well as educators looking for practical examples of motion problems.

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Homework Statement



The driver of a pick up truck going 100 km/h applies the brakes, giving the truck a uniform deceleration of 6.5m/s(squared) while it travels 20.0 m
a) what is the speed of the truck in km/h at the end of tihs distance
b) how much time has elapsed

her is the thing i have the answers but no way of showing my work and with the change in units km/h m/s i get mixed up PLEASE HELP!

answers
a) 81.4 km/h
b) 0.794 s
 
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Ok so what would you do first for a)?

what formula would you use to solve for the final speed of the truck?

also I think you need to do b) before you can do a).

so what equation can you use to solve for the time elapsed?

When you're going to change the units just make sure to show your work really good in order to spot an error.

Other than that I don't think I can help you out more without giving the answer away.
Just show some work even if you do it wrong at least we'll see if you are going on the right track and just messed up on units/etc...
 
a)
try the formula u^2 = v^2 + 2as
where u=initial velocity, v=final velocity, a=acceleration (will be a negative), and s=the distance traveled.

b)
try using v = u + at
using the final velocity that you found in section a.
t will give you time.
 

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