How Do You Calculate Frictional Force in a Braking Scenario?

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To calculate the frictional force in a braking scenario, first determine the car's final velocity before braking, which is 18 m/s. Using the kinematic equation, the deceleration can be calculated from the initial velocity and the stopping distance of 50 m. The average frictional force can then be found using Newton's second law, where the force equals mass times acceleration. The discussion highlights the importance of understanding initial and final velocities, as well as how to apply kinematic equations effectively. Clarifying these concepts is essential for accurately solving the problem.
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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.
 
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you have distance, initial velocity, final velocity and solving for acceleration. Solve the kinematic equation that doesn't have time.
 
Lami said:
I'm confused with how to go about tackling c and was wondering how to tackle it?
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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