Given,
The speed of the family car, S1=50 miles/h
The speed of the sports car, S2=70 miles/h.
The family car left the starting position t=2 hours earlier.
So, the distance between the family car and the sports car when the sports car starts is,
The sports car has to overcome this 100 mile distance to overtake the family car.
The relative speed of sports car with respect to the family car is,
So, the time taken by the sports car to overcome the family car is,
Therefoe, the sports car takes 5h to overcome the family car.