A car travels at a speed of 40 m/s for two hour and then at 60 m/s for

1.	A car travels at a speed of 40 m/s for two hour and then at 60 m/s for 4 hours. What is the average speed of the car (in m/s) during the entire journey?
Answer» Answer: Let the DISTANCE for outward journey = d metre Time taken to travel the distance d metre at a speed of 40m/s = d/40 second Time taken to travel distance d on the return journey at a speed of u m/s = d/u second Total time taken for the outward and return JOURNEYS = (d/40) + (d/u) = d( 1/40 + 1/u) = d [(u + 40)/40 u] Total distance travelled = d +d = 2 d metre Average speed = (Total distance travelled) ÷total time taken = 2d ÷ d (u +40)/40 u = 80 u/ u +40 = 48 => 80 u = 48 u + 48 × 40 => 80 u - 48 u = 48 × 40 => 32 u = 48 × 40 => u = (48 × 40)/32 = 3 × 20 = 60 m/s. u = 60 m/s.

A car travels at a speed of 40 m/s for two hour and then at 60 m/s for 4 hours. What is the average speed of the car (in m/s) during the entire journey?

Answer»

Answer:

Let the DISTANCE for outward journey = d metre

Time taken to travel the distance d metre at a speed of 40m/s = d/40 second

Time taken to travel distance d on the return journey at a speed of u m/s = d/u second

Total time taken for the outward and return JOURNEYS = (d/40) + (d/u) = d( 1/40 + 1/u) = d [(u + 40)/40 u]

Total distance travelled = d +d = 2 d metre

Average speed = (Total distance travelled) ÷total time taken = 2d ÷ d (u +40)/40 u = 80 u/ u +40 = 48

=> 80 u = 48 u + 48 × 40

=> 80 u - 48 u = 48 × 40

=> 32 u = 48 × 40

=> u = (48 × 40)/32 = 3 × 20 = 60 m/s.

u = 60 m/s.