Answer to Question 6

a    The deceleration = 0 - 60 = - 60 ÷ 25 = -2.4 m s^-2
                                     25

b   Braking force = mass × acceleration =  5000 × -2.4 = 12 000 N

c    s = 60 × 25 + 1/2(-2.4 × 25²) = 750 m.

Did you remember to use the fact that the acceleration was negative?