Question

A bar magnet is tied to a string and hung from the ceiling. Gravitational force of attraction by the earth is pulling the magnet down. According to Newton's first law, the magnet should move towards ground as it is acted upon by a force. Then why isn't it happening.

• A. Repulsion by Earth's Magnetic field holds it in air
• B. The volume of air displaced gives a Buoyant force to hold it up
• C. Air friction is balancing the magnet
• D. The tensile strength of the string is balancing the gravitational pull by earth.

Answer 1

The correct option is D

The tensile strength of the string is balancing the gravitational pull by earth.

First things first.

Can we even apply newton's law in this case.

I think yes, we are talking about earth's surface which is close enough to be termed as inertial frame.Okay then

From first law we know net force should be zero.

Let's look at our options

(a) Earth's magnetic repulsion holds the magnet. Yeah right!!

If that were true then no magnet would ever fall to the ground.

(b) Air's buoyant force . . . . . seriously. Then I should be floating too as I am fat.

(c) Air friction. What was I thinking while making this question. Its impossible !

(d) strings tension. Finally something that makes sense.

There is tension in the rope that is holding up the block.