Kinematics truck moving at 30m/s suddenly notices a moose 70m

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SUMMARY

The discussion centers on a kinematics problem involving a truck traveling at 30 m/s that must stop to avoid hitting a moose 70 meters ahead. The driver has a reaction time of 0.5 seconds and a maximum deceleration of 8 m/s². Calculations show that the total stopping distance, including reaction time, is 55.25 meters, which is insufficient to avoid the moose. The correct approach requires treating the reaction time and braking distance as separate segments of motion to accurately determine the total distance covered before stopping.

PREREQUISITES
  • Understanding of kinematic equations, specifically for uniformly accelerated motion.
  • Knowledge of concepts such as reaction time and deceleration.
  • Ability to perform calculations involving distance, speed, and time.
  • Familiarity with the formulae: v = u + at and s = ut + 1/2at².
NEXT STEPS
  • Study the separation of motion segments in kinematics problems.
  • Learn about the implications of reaction time on stopping distances.
  • Explore real-world applications of kinematics in vehicle safety and stopping distances.
  • Practice additional problems involving deceleration and reaction time scenarios.
USEFUL FOR

This discussion is beneficial for students studying physics, particularly those focusing on kinematics, as well as educators looking for practical examples to illustrate motion concepts.

monkfishkev
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Homework Statement


The driver of a truck moving at 30m/s suddenly notices a moose 70m straight ahead. If the driver's reaction time is 0.5s and the maximum deceleration is 8m/s^2, can he avoid hitting the moose without steering to one side?


The Attempt at a Solution


First I found out how long it would take the driver to stop.
v = u + at
0 = 30 -8t
t = 3.75

I then added the drivers reaction time of 0.5s so we land up with 4.25s

Then I tries to fid out the distance covered by using:
s = ut + 1/2at^2
s = 30(4.25) + 1/2(-8)(4.25)^2
s = 127.5 - 72.25
s = 55.25m

It would seem that the truck stops before 70m but the answer given in the book says no he doesn't stop in time and needs a further 1.3m.

Please help.
 
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monkfishkev said:
I then added the drivers reaction time of 0.5s so we land up with 4.25s
Instead of adding the times together, treat the two segments of motion separately. Hint: How far does he get before he steps on the brakes?
 

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