Unbalanced force

  • Thread starter zoezoehzoe
  • Start date
  • #1

Homework Statement



A car has a mass of 1350 kg and an initial speed of 21 m s-1. Calculate the magnitude of the unbalanced force applied to the brakes that caused the car to come to a halt in 3 seconds.

Homework Equations



Force = mass x acceleration,
= ( 1350 kg ) x ( -7 m s-2 ),
= -9450 kg m s-2
= -9450 N

My question is this, is it ok to write the answer as a negative value of newtons, as above, because it doesn't seem right? I'm a little confused, any advice would be appreciated.

The Attempt at a Solution

 

Answers and Replies

  • #2
Doc Al
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My question is this, is it ok to write the answer as a negative value of newtons, as above, because it doesn't seem right? I'm a little confused, any advice would be appreciated.
Magnitudes are always positive. In this case, the negative sign just indicates the direction--that the acceleration and force were opposite to the velocity.
 
  • #3
Magnitudes are always positive. In this case, the negative sign just indicates the direction--that the acceleration and force were opposite to the velocity.
so

Force = mass x acceleration,
= ( 1350 kg ) x ( -7 m s-2 ),
= -9450 kg m s-2
= 9450 N

would be correct?
 
  • #4
Doc Al
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45,029
1,326
Yes. Your answer would just be the magnitude--leave off any sign.
 
  • #5
Yes. Your answer would just be the magnitude--leave off any sign.
thank you very much for your help.
 

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