Question

Question 12 According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.

Class 9 - Science - Force and Laws of Motion Page 129

Answer 1

Student's justification is not correct . Two equal and opposite forces cancel each other if they act on the same body.

According to the third law of motion, Action and Reaction forces are equal and opposite but they both act on different bodies. Hence, they cannot cancel each other.


When we push a massive truck, then the force applied on the truck is not sufficient to overcome the force of friction between the tyres of the truck and ground.


Hence, the truck does not move . The truck will move only if the force applied on it is greater than the frictional Force.

Answer 2

Answer:

Third law of motion states that every action has equal and opposite reaction.

Explanation:

The justification given by student is not correct as action and reaction always act on different bodies, so they can not cancel each other.

A truck standing in roadside has heavy weight and more friction force between tyres and ground than the push exerted. So, the truck will only move when a force more than friction force will be applied on the truck.

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