A car of mass 1000 kg travels at 20 m/s. The driver sees a stationary obstacle 40 m ahead and reacts for 0.50 s. A constant resultant braking force of 5000 N then acts. What is the speed of the car when it reaches the obstacle?
0 m/s0\ \mathrm{m/s}0 m/s
5 m/s5\ \mathrm{m/s}5 m/s
10 m/s10\ \mathrm{m/s}10 m/s
15 m/s15\ \mathrm{m/s}15 m/s