A car is moving along a straight line in the given figure 1.83. It moves from O to P in 18 seconds and returns from P to Q in 6 seconds . What are the average velocity and average speed of the car in going (a) from Q to P ? And (b) from O to P and back to Q ?

Explanation

For the motion from O to P, distance travelled = displacement
= OP = (360-0) = 360 m
So, average speed = `("distance travelled")/("time")`= average velocity
This average speed or velocity is
v =` (360 m)/(18 s) 20 "m.s"^(-1)`
Now for this motion from O to P and back to Q , distance travelled = OP+PQ
= 360+(360-240) = 480 m
So, average speed = `(480m)/((18+6)s) = 20 "m.s"^(-1)`
But displacement = `oversetto(OP)+oversetto(PQ)=oversetto(OQ)`, whose magnitude =240 m and the time taken = 18 +6 =24 s.
Hence average velocity = `(240 m)/(24 s)10 "m.s"^(-1)`