Physics Part I

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Class 10 Class 12

A 0.5 kg ball moving with a speed of 12 m/s strikes a hard wall at an angle of 30° with the wall. It is reflected with the same speed and at the same angle. If the ball is in contact with the wall for 0.25 s, the average force acting on the wall is

• 48 N

• 24 N

• 12 N

• 96 N

B.

24 N

The vector  represents the momentum of the object before the collision, and the vector  that after the collision. The vector  represents the change in momentum of the object .

As the magnitudes of   are equal, the components of  along the wall are equal and in the same direction, while those perpendicular to the wall are equal and opposite. Thus, the change in momentum is due only to the change in direction of the perpendicular components.
Hence,

Its time rate will appear in the form of average force acting on the wall.

The vector  represents the momentum of the object before the collision, and the vector  that after the collision. The vector  represents the change in momentum of the object .

As the magnitudes of   are equal, the components of  along the wall are equal and in the same direction, while those perpendicular to the wall are equal and opposite. Thus, the change in momentum is due only to the change in direction of the perpendicular components.
Hence,

Its time rate will appear in the form of average force acting on the wall.

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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.
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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.
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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.
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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.
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Is Aristotle’s law of motion now correct?

No. Aristotl'e law of motion is false.
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