Shortcut Trick
Speed of B = Distance gap ÷ Time gap = 50 m ÷ 5 s = 10 m/s.
Time taken by B to finish the race = 1000 m ÷ 10 m/s = 100 s.
Time taken by A = 100 s − 5 s = 95 s.
Speed of A = 1000 m ÷ 95 s = 200/19 m/s.
Speed Difference = Speed of A − Speed of B = 200/19 − 10 = (200 − 190)/19 = 10/19 m/s.
∴ The correct answer is 10/19 m/s.
Alternate Method
Given:
Total Race Distance = 1000 m
A beats B by distance = 50 m
A beats B by time = 5 s
This implies that when A finishes the race (covers 1000 m), B is 50 m behind the finish line and takes 5 seconds more to cover that distance.
⇒ Speed of B = Distance covered ÷ Time taken = 50 m ÷ 5 s = 10 m/s
⇒ Time taken by B to complete 1000 m = 1000 m ÷ 10 m/s = 100 s
⇒ Time taken by A to complete 1000 m = Time of B − Time gap = 100 s − 5 s = 95 s
⇒ Speed of A = Total Distance ÷ Time of A = 1000 m ÷ 95 s = 200/19 m/s
⇒ Difference in speeds = Speed of A − Speed of B = (200/19) − 10
⇒ Difference = (200 − 190) ÷ 19 = 10/19 m/s
∴ The correct answer is 10/19 m/s.
Additional Information
Fundamental Motion Formula
The core relationship in problems involving movement is: Speed = Distance ÷ Time.
Concepts of Beating in Races
If A beats B by 'd' meters, then when A covers L distance, B covers (L − d). If A beats B by 't' seconds, then B's total time is TimeA + t.
Relative Speed
When two objects move in the same direction, their relative speed is the difference of their individual speeds (V1 − V2).