A car is moving along a straight line, say OP in Fig. It moves from O to P in 18 s and returns from P to Q in 6.0 s. What are the average velocity and average speed of the car in going (a) from O to P ? and (b) from O to P and back to Q ?

Explanation

a) Average velocity = `"Displacement"/"Time interval"`
`bar(upsilon)=(+360m)/(18s)=+20ms^(-1)`
Average speed = `"Path length"/"Time interval"`
`" "=(360m)/(18s)=20ms^(-1)`
Thus, in this case the average speed is equal to the magnitude of the average velocity.
b) In this case,
Average velocity `="Displacement"/"Time interval"`
`" "=(+240m)/((18+6.0)s)=+10ms^(-1)`
Average speed `="Path length"/"Time interval"`
`" "=(OP+PQ)/(Deltat)`
`=((360+12)m)/(24s)=20ms^(-1)`