In a 100 m race, A runs at 6 km/hr. A gives B a start of 4 m and still beats him by 4 sec. Find the speed of B.
Speed of A = 6 km/hr
=$6\times\dfrac{5}{18}$
=$\dfrac{5}{3}m/s$
Time taken by A = $\dfrac{distance}{speed}$
=$\dfrac{100}{\left(\dfrac{5}{3}\right)}$
=60sec
A gives B a start of 4 m
i.e., B has to cover (100-4)
=96 metre
A beats B by 4 sec
=> Time taken by B to run the race = 60 + 4
= 64 sec
Speed of B =$ \dfrac{Distance}{Time}$
=$\dfrac{96}{64}m/s$
=$\dfrac{96}{64}\times\dfrac{18}{5}$
=5.4 km/hr