Home » 2011 » August

# Monthly Archives: August 2011

### Subscribe to this site by email ## Resultant magnetic force

What is resultant magnetic force? can you please explain with an example.

(Shreya)

When a magnetic substance (or a magnet) is placed in a region where there are multiple magnetic fields, the net force due to all of them is called the resultant.

In other words, it is that magnetic force which can effectively replace all other magnetic force acting on it

(Need more explanation? Post as comment to this post for details)

## Coulombian force and conductor

what’s effect of  coulombic forces on conductor medium ?

amk niazi

Ans:

In a conductor, the coulombian  repulsive forces  pushes the valence electrons and the electrons move away from the center to the surface ie from the region of stronger force to the region of lesser force, creating a Faraday cage

## The question of minimum time and minimum distance in crossing a river.

A man crosses a river in a boat if he crosses the river in minimum time he take 10min with a drift 120metre if he crosses the river taking shortest path he takes 12.5min find the width of the river

## Magnetism and Laws of motion

“Can a body at rest make another body move,according to the laws of Newton this is impossible. The question is in magnetism, If it happens then why is it not predicted by classical mechanics?”

Answer: First of all I congratulate you for your genuine thought. It is the critical thinking which will lead you to great discoveries.

To answer your question, let me ask you the question – When an apple falls to earth, the earth is also attracted by the apple by an equal and opposite force, then why earth is not moving towards the apple?

The difference lies in the acceleration achieved.  a= F/m

Since mass of earth is very much large, its acceleration towards apple is negligibly small compared to the acceleration due to gravity (9.8 m/s2)

When the magnet attracts another magnet or a magnetic substance, both are experiencing the same force. But it is common that we generally hold the magnet restricting its motion. Therefore, it is not able to move towards the other one.

Newton’s third law is valid and correct even if the forces are contact forces or non contact forces.

## Solving problems on Laws of Motion

Sir,in solving problems of laws of motion ,is it mandatory to take that direction as +ve in which acceleration acts?(i.e should i subtract other forces acting on a body from the forces that is acting towards the acceleration)

Answer: In general, we take the forces in the direction of acceleration (I.E, ENHANCING THE ACCELERATION) and the forces against the acceleration as negative.

The first step in solving such problems is to draw a free body diagram and represent all active forces and reactions to constraints in vector form with proper direction ad label. This will highly simplify the problem.

## Path of an object

If a man tossed a coin in a moving train and the coin fell back . Then in which type of motion train is moving? and how?

CHANDRIMA

For the person who tosses the coin the motion is vertically upward if he do so. But for an observer outside the train the path of the stone is a parabola.This is due to the horizontal velocity of the stone.

If the stone fell back, it means that the train is accelerated. If it were moving with a constant velocity, then the stone would’ve reached back to his hands only as both the train and the stone possess the same horizontal velocity.

## Acceleration due to gravity

Does the acceleration due to gravity remains constant within the earth’s atmosphere or does it keep decreasing as we go up from the earth’s surface?

No acceleration due to gravity decreases as we go up from the earth’s surfacs

### Hits so far @ AskPhysics

• 2,239,549 hits