Question

A car moving 30m/s slows uniformly to a speed of 10 m/s in a time of 5 sec determine
1) the acceleration of the car
2) the distance it moved in 3 sec

Answer 1

since v decreased by 20m/s in 5 sec, a = -4 m/s^2

assuming the 3 seconds started at t=0,
s = 30t - 2t^2
s(3) = 30(3) - 2(9) = 72m

Answer 2

correct answer
a = -4 m/s^2
s = 72 m

Answer 3

Soln to a) a=V-U/t=10-30/5=-4m/s^2 Soln to b) S1= ut+1/2at^2=30*3+1/2*-4*3*3=72m ,t=5-3=2 S2=ut+1/2at^2=10*2+1/2*-4*2*2=52m so, ST= S1+S2=72+52=124m