Question

A car travel from stop a to stop be with a speed of 30 km per hour and then return back with a speed of 50 km per hour: a) Displacement of the car b) Distance travelled by the car c) Average Speed of the car ​

Answer 1

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Let the distance from A to B be x

The displacement of the car is zero because car comes back to the same position and we know that displacement is the shortest distance between initial and Final point of moving object with particular direction.

Then,

The distance travelled = 2x

Time taken by the car when it moves from A to B and from B to A

• $\bf\:t_1=\dfrac{Distance}{Speed}$

• $\bf\:t_1=\dfrac{x}{30}$

• $\bf\:t_2=\dfrac{Distance}{Speed}$

• $\bf\:t_2=\dfrac{x}{50}$

Total distance = 2x

$\bf\:Total\:time=t_2+t_2$

$\bf\:Total\:time=\dfrac{x}{30}+\dfrac{x}{50}$

$\bf\:Total\:time=\dfrac{5x+3x}{150}$

$\bf\:Total\:time=\dfrac{8x}{150}$

then,

$\bf\:Average\:speed=\dfrac{Total\:distance}{Total\:time}$

$\bf\:Average\:speed=\dfrac{2x}{8x/150}$

$\bf\:Average\:speed=2x\times\:\dfrac{150}{8x}$

$\bf\:Average\:speed=\dfrac{150}{4}$

$\bf\green{{Average\:speed=37.5\:km/h}}$