Question

If a body covers first half of its journey with uniform speed 40m/s and the second half with a speed 10m/s then the average speed is
1)80m/s
2)60m/s
3)50m/s
4)40m/s​

Answer 1

Given :

Body covers first half of the total distance at a speed of 40m/s amd second half of the total distance at a speed of 10m/s.

To Find :

Average speed of body.

Solution :

If body covers first half of the total distance at a speed of $\sf{v_1}$ and second half of the total distance at a speed of $\sf{v_2}$ then average speed of body is given by

$\bigstar\:\underline{\boxed{\bf{v=\dfrac{2v_1v_2}{v_1+v_2}}}}$

Let's calculate ☃

$\mapsto\tt\:v=\dfrac{2v_1v_2}{v_1+v_2}$

$\mapsto\tt\:v=\dfrac{2(40)(10)}{40+10}$

$\mapsto\tt\:v=\dfrac{800}{50}$

$\mapsto\underline{\boxed{\bf{v=16\:ms^{-1}}}}$

[Kindly check the options :D ]