Question

A car covers half the distance at a speed of 50km/hr and the other half at 40 km/hr. find the average speed of a car. (44.44 km/hr)
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Answer 1

Answer:

$\boxed{\bold{Average\:speed=44.4\:km/hr}}$

Explanation:

$\Large{\underline{\underline{\bf{Given:}}}}$

• Speed of the car in the first part of the journey = 50 km/hr
• Speed of the car in the second part of the journey = 40 km/hr

$\Large{\underline{\underline{\bf{To\:Find:}}}}$

• Average speed of the car

$\Large{\underline{\underline{\bf{Solution:}}}}$

→ Let half of the distance be x. Therefore other half is also x

→ Time taken in the first part of the journey is given by

   Time  = Distance/ Speed

   Time = x/50 hrs

→ Time taken in the second part is,

   Time = x/40 hrs

→ Average speed is given by the formula,

  Average speed = Total distance travelled/ Total time taken

  $Average speed=\dfrac{x+x}{\dfrac{x}{50}+\dfrac{x}{40} }$

  $Average speed=\dfrac{2x}{\dfrac{90x}{2000} }$

→ x gets cancelled on both numerator and denominator

 Average speed = 2 / 0.045

 Average speed = 44.4 km/hr

$\boxed{\bold{Average\:speed=44.4\:km/hr}}$

$\Large{\underline{\underline{\bf{Notes:}}}}$

→ Speed is defined as the distance travelled per unit time. It's SI unit is m/s.

→ Speed is a scalar quantity.