Question

A motorcycle drives from A to B with a uniform speed of 30 km/h and return back with a speed of 20 km/h. Find the average speed

Answer 1

A motorcycle drives from A to B with a uniform speed of $30\mathrm{km/h}$ and return back with a speed of $20\mathrm{km/h}$. Find the average speed

Solution:

Let $v_{avg}$-average speed.

Let $v_{1} = 30\frac{km}{h}, v_{2} = 20\frac{km}{h}$

Let S – distance from A to B

Time taken from A to B is $t_1 = \frac{S}{v_1}$

Time taken from B to A is $t_2 = \frac{S}{v_2}$

Total distance travelled is: 2S

So

$$v_{avg} = \frac{2S}{\frac{S}{v_2} + \frac{S}{v_2}} = 2\frac{v_1 v_2}{v_1 + v_2} = 24\ \mathrm{km/h}$$

Answer: $24\ \mathrm{km/h}$