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Laws of Motion

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Physics Part I

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
A bob of mass 0.1 kg hung from the ceiling of a room by a string 2 m long is set into oscillation. The speed of the bob at its mean position is 1 m s–1. What is the trajectory of the bob if the string is cut when the bob is
(a) at one of its extreme positions,
(b) at its mean position.

(a) When bob is at its extreme position:

The trajectory of the bob if the string is cut at one of it's extreme positions will be in vertically downward direction.

At the extreme position, the velocity of the bob becomes zero. If the string is cut at this moment, then the bob will fall vertically on the ground. 

(b) When the bob is at its mean position:

When the string is cut at its mean position, the trajectory of the bob will be a parabolic path. 
At the mean position, the velocity of the bob is 1 m/s.

The direction of this velocity is tangential to the arc formed by the oscillating bob. If the bob is cut at the mean position, then it will trace a projectile path having the horizontal component of velocity only.

Hence, the bob will follow a parabolic path. 

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. 

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. 

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.

Is Aristotle’s law of motion now correct?

No. Aristotl'e law of motion is false. 

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.