Question

Two wheels of diameter 7 cm and 14 cm start rolling simultaneously from two points A and B which are 1980 cm apart each other in opposite towards directions. Both of them make same number of revolutions per second. If both of them meet after 10 seconds, the speed of bigger wheel is

• A. 88 cm/s
• B. 110 cm/s
• C. 132 cm/s
• D. 154 cm/s

Answer 1

Answer:

C. 132 cm/s

Solution:

Given:

Diameter of wheel (r) = 7cm

Diameter of other wheel (r') = 14cm

Rolling in opposite direction in two points = 1980 cm apart

Number of revolution both makes same.

Both meet after 10 seconds

Calculation:

Radius of wheels are : 7/2cm, 7cm.

Let each wheel makes x revolution per sec.

∴ [(2π × 7/2 × x) + (2π × 7 × x)] × 10 = 1980

⇒ [(14π x + 28π x)] = 198 × 2

⇒ 21π x = 198

x = 198 × 7/(22 × 21) = 3

∴ Speed of bigger wheel = 2π × 7 × 3 = 132 cm/sec