﻿ A disc revolves with a speed of  rev/min, and has a radius of 15 cm. Two coins are placed at 4 cm and 14 cm away from the centre of the record. If the coefficient of friction between the coins and the record is 0.15, which of the coins will revolve with the record? from Physics Laws of Motion Class 11 Manipur Board

## Book Store

Currently only available for.
`CBSE` `Gujarat Board` `Haryana Board`

## Previous Year Papers

Download the PDF Question Papers Free for off line practice and view the Solutions online.
Currently only available for.
`Class 10` `Class 12`
A disc revolves with a speed of  rev/min, and has a radius of 15 cm. Two coins are placed at 4 cm and 14 cm away from the centre of the record. If the coefficient of friction between the coins and the record is 0.15, which of the coins will revolve with the record?

Coin placed at 4 cm from the centre

Given,

Mass of each coin = m

Radius of the disc, r = 15 cm = 0.15 m

Frequency of revolution, ν = rev/min

=

=  rev/s
Coefficient of friction, μ = 0.15

In the given situation, the coin having a force of friction greater than or equal to the centripetal force provided by the rotation of the disc will revolve with the disc. If this is not the case, then the coin will slip from the disc.

Case 1: Coin placed at 4 cm

Radius of revolution, r' = 4 cm = 0.04 m

Angular frequency, ω = 2πν

= 2 x
= 3.49 s-1

Frictional force, f = μmg

= 0.15 × m × 10

= 1.5m N

Centripetal force on the coin is,

Fcent. = mr'ω

= m × 0.04 × (3.49)

= 0.49 m N

Since f > Fcent, the coin will revolve along with the record.

Case 2: Coin placed at 14 cm

Radius, r" = 14 cm = 0.14 m

Angular frequency, ω = 3.49 s–1

Frictional force, f' = 1.5 m N

Centripetal force is given as,

Fcent. = mr"ω

= m × 0.14 × (3.49)2

= 1.7m N

Since f < Fcent., the coin will slip from the surface of the record.
163 Views

What is Aristotle’s law of motion?

Aristotle’s law of motion states that an external force is required to keep the body in motion.
2445 Views

State Galileo’s law of motion.

Galileo’s law of motion states that, a body continues to move in the same direction with constant speed, if no force is acting on the body.
1332 Views

When the branches of an apple tree are shaken, the apples fall down. Why?

The apple fall from an apple tree when it shaken because of inertia of rest. Apple is in a state of rest and when the tree is suddenly shaken, apples still tends to remain in it's same state of rest whereas branches move.

So, the apples fall down.
1475 Views

Is Aristotle’s law of motion now correct?

No. Aristotl'e law of motion is false.
1233 Views

Define inertia.

The property by virtue of which the body cannot change its state of rest or uniform motion in a straight line, unless an external force is acting on the body is called as Inertia.
1316 Views