A vehicle covers certain distance at constant speed of `20 km h^(-1)` in time interval 't' on linear path. Then it covers certain distance at constant speed of `30 km h^(-1)` in the same time interval. What is the average speed of the vehicle ?

Explanation

Here `v _(j) v _(g) and v _(0)` are velocities of jet plane, combustion products ejected and observer on ground respectively.
Suppose, jet plane is moving in +X-axis,
Ejected combustion products are in -X-axis,
Now `v _(j) = 500` km/hr
`v _(0) = 0` (At rest)
Velocity of jet plane w.r.t observer,
`=v _(j)- v _(0) = 500 -0`
` = 50 km//hr. " "...(1)`
Velocity of combustion products w.r.t jet plane,
`v _(g) -v_(j) = - 1500 km.//hr." "...(2)`
`v _(g) - v _(0) = 500 - 1500 = - 1000 km//hr`
Velocity of ejected combustion products by observer on ground in opposite to jet plane is 1000 km/hr.