Question

A mman runs round a circular field of radius 50 m at a speed of 12 km/hr. What time is taken by the man to make twenty rounds of the field?
(a) 30 min.
(b) 32 min.
(c) 34 min.
(d) 31 3/7​

Answer 1

Given :

• Radius of circular field = 50 m
• Speed of man = 12 km/h

To find :

• Time taken to make 20 rounds of the field

Solution :

Speed of man = 12 km/h

                        = 12 * (5/18) m/s

                         = 3.33 m/s

Now we know,

Distance = Speed * Time

Now as the field is circular, so distance covered in 1 round is equal to circumference of field.

⇒ Distance covered in 1 round = 2πr

⇒ Distance covered in 20 rounds = 20 * 2 * 3.14 * 50

⇒ Distance covered in 20 rounds = 2000 * 3.14

⇒ Distance covered in 20 rounds = 6280 m

Now using distance formula :

⇒ 6280 = 3.33 * time

⇒ Time = 6280/3.33

⇒ Time = 1885.89 s

⇒ Time = 1885.89/60 m

⇒ Time = 31.43 m

⇒ Time = (31 + 0.43)

⇒ Time = (31 + 3/7) m

⇒ Time = 31 3/7 m

Therefore,

Time taken to complete 20 rounds = 31 3/7 m