Determine the time it take for the car and the truck to meet

  • Thread starter Arden
  • Start date
  • #1
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a car starts from rest at a point 300m from a truch that is moving at a constant rate of 30m/s toward the car. IF the car accelerates at .8m/s2, determine the time it take for the car and the truck to meet.
s=300
This is what I did
Car:
Vi = 0, a = .8
Vf^2=2as = Vf=21.9

Vf=at
21.9/.8 = 27.38
t=27.38sec

Truck:
S=(V/2)t
S=(15)t
300/15 = 20
t=20

They meet after (27.38 -20) = 7.38 seconds.

The answer given is 8.94seconds. Not sure what I am doing wrong?????
 

Answers and Replies

  • #2
James R
Science Advisor
Homework Helper
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15
You assumed the truck meets the car at 300 m. It doesn't, because the truck is moving towards the car.
 
  • #3
Pyrrhus
Homework Helper
2,178
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You will need to set up your equation such as the car will cover a distance x, which will be the distance the truck meets the car, but the truck will cover a distance x+300.
 
  • #4
208
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dont you mean 300 - x
 
  • #5
Pyrrhus
Homework Helper
2,178
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Depends on where you put your coordinate system, i put the origin on the car.
 
  • #6
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Thank you all for your help - Arden
 

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