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Very basic question about forces

  1. Sep 21, 2016 #1
    • Homework template is missing because this was originally posted in a non-homework forum
    I'm very new to physics and am doing a crash higher course. I am currently tackling dynamics, and here is one of the questions I was given.
    8 ) A car of mass 800kg is accelerated from rest to 18m/s in 12 seconds.
    a) What is the size of the resultant force acting on the car
    b) How far does it travel in these 12 seconds?
    c) At the end of 12 seconds period the brakes are operated and the car comes to rest in a distance of 50m. What is the size of the average frictional force acting on the car?

    I got for a) F=ma =800 x 1.5 = 1200N For b) s= ut+ 1/2at^2 = 0.5 x 1.5 x 144 = 108m. I'm confused with how to go about tackling c and was wondering how to tackle it? Apologies in advance for if it's blarringly obvious.
  2. jcsd
  3. Sep 21, 2016 #2
    you have distance, initial velocity, final velocity and solving for acceleration. Solve the kinematic equation that doesn't have time.
  4. Sep 21, 2016 #3


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    What is the final velocity in part c? What is the velocity at the instant of application of brakes? Can you calculate the deceleration from this?
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