Question

The radius of the wheel of a vehicle is 70 cm. The
wheel makes 10 revolutions in 5 seconds. The
speed of the vehicle is
(A) 29.46 kmph
(B) 31.68 kmph
(C) 36.25 kmph
(D) 32.72 kmph​

Answer 1

$\tt\huge \: \underline {Given}: \:$

• The roots of wheel 70 cm.
• The wheel makes 10 revolutions in 5 sec.

$\tt\huge \: \underline {To \: Find}: \:$

• Find the speed of the vehicle.

$\tt\huge \: \underline {Solution}: \:$

The circumference of circles = 2πr

$\tt\implies \: 2 \times \dfrac{22}{7} \times 70$

$\tt\implies \: 44 \times 10$

$\tt\implies \: 440cm$

Distance travelled in 10 revolution is

$\tt\implies \: 440 \times 10$

$\tt\implies \: 4400cm$

$\tt\implies \: 44m$

Now,

$\tt\implies \: Speed = \dfrac{distance}{time}$

$\tt\implies \: Speed = \dfrac{44}{5}$

$\tt\implies \: Speed = 8.8m/s$

Convert m/s to km/h:

$\tt\implies \: 8.8 \times \dfrac{18}{5}$

$\tt\implies \: 31.68km/h$

Answer 2

Correct option

(B) 31.68 kmph

Distance covered in 5 sec :

= (2 × 227 × 70 × 10)cm = 4400cm =44m

Distance covered in 1 sec :

= (445) m= 8.8m =(445)m = 8.8m

∴ Speed : =8.8m/sec = (8.8×185)km/hr = 31.68km/hr