Help with Physics please?

Question

A speeding car is traveling at a constant speed of 10.0 m/s when it passes a stopped police car. the police car accelerates at 7.0 m/s^2. How fast will it be going when it catches up with the speeding car?

Answer 1

S1=S2 when the police car catches up both of them would cover the same distance

S1=V1t (for the speeding car V1=10m/s)
S2=0.5at^2 (for police car)
so
V1t=0.5at^2
t=2V1/a

V=at
V=a (2V1/a)
V=2V1
V=20 m /s