Question

- A motorcyclist drives A to B with a uniform speed of 30 kmph and returns back with a speed of 20 kmph. Find the its average speed a) 20 kmph b) 24 kmph c) 42 kmph d) 52 kmph

Answer with solution​

Answer 1

Answer:

b) 24 kmph

Explanation:

Let the length of the line segment AB be x m

The time taken is given as t=distance covered/speed

Total time = t1+t2=30x+20x=605x h

Average speed = Total distance/Total time = 5x/602x=24 km/h

Answer 2

Required Answer:-

The distance between A and B will remain same. So the distance traveled by the motorcyclist on his way and back is the same. Let the distance traveled by the motorcylist from A to B be S.

From A to B:

• Distance travelled = S
• Speed of the motorcyclist = 30 km/hr.
• Time taken = S/30 hr

From B to A:

• Distance travelled = S
• Speed of the motorcyclist = 20 km/hr.
• Time taken = S/20 hr

We know,

Average speed = Total distance/Total time taken

Putting the values in the formula

$= \rm{\dfrac{s + s}{ \dfrac{s}{30} + \dfrac{s}{20} } km {hr}^{ - 1} }$

$= \rm{ \dfrac{2s}{s( \dfrac{5}{60}) } km {hr}^{ - 1} }$

$= \rm{\dfrac{2 \times 60}{5} km {hr}^{ - 1} }$

$= \red{\boxed{ \blue{\rm{24 \: km {hr}^{ - 1} }}}}$

The average speed of the body is 24 km/hr (B)

Note:-

• Simple trick for finding average speed when distance is same: 2v1.v2 / v1 + v2