B. A car moving at an initial speed vi applies its brakes and skids for some distance until coming to a complete stop. If the coefficient of kinetic friction between tires and the road is µk what distance did the car skid?

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Complete Question

The complete question is  shown on the first uploaded image  

Answer:

The distance which the car skid is  [tex]l = \frac{v_i^2 }{2 * \mu_k * g }[/tex]

Explanation:

From the question we are told that  

     The  initial velocity of the car is  [tex]v_i[/tex]

     The  coefficient of kinetic friction is  [tex]\mu_k[/tex]

According to the law of energy conservation

    The initial Mechanical Energy =  The final  Mechanical Energy  

                           [tex]M_i = M_f[/tex]  

The initial mechanical energy is  mathematically represented as  

              [tex]M_i = KE _o + PE_e[/tex]

where KE is the initial kinetic energy which is  mathematically represented as

        [tex]KE = \frac{1}{2} m v_i^2[/tex]

And  PE  is  the initial potential energy which is  zero given that the car is  on the ground

     Now  

           [tex]M_f = W_{\mu}[/tex]

Where  [tex]W_{\mu}[/tex] is  the work which friction exerted on the car  which is  mathematically represented as

       [tex]W_{\mu} = m* \mu_k * g * l[/tex]

Where  [tex]l[/tex] is the distance covered by the car before it slowed down

        [tex]\frac{1}{2} m v_i^2 = m* \mu_k * g * l[/tex]

=>     [tex]l = \frac{v_i^2 }{2 * \mu_k * g }[/tex]

                 

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