9. Force and Laws of Motion – Class 9 Science | NCERT Chapter-wise Important Questions and Answers (CBSE)

Chapter 9: Force and Laws of Motion – Class 9 Science NCERT | Chapterwise Important Questions and Answers (CBSE)

Chapter 9: Force and Laws of Motion

Questions
1. Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five- rupees coin and a one-rupee coin?

Answer: (a) The stone has more inertia than the rubber ball because it is denser and heavier.

(b) The train has more inertia than the bicycle because it is larger and has more mass.   

(c) The five-rupees coin has more inertia than the one-rupee coin because it is heavier.

Or

Inertia is the property of an object that resists changes in its state of motion. It depends on the mass of the object.

(a) In this case, if the rubber ball and the stone are of the same size, it means they have the same volume. However, their masses can be different because the density of rubber and stone can vary. Therefore, the object with more mass will have more inertia. Without specific information about their masses, we cannot determine which object has more inertia.

(b) A train typically has a much greater mass than a bicycle. Since inertia depends on mass, the train will have more inertia than the bicycle.

(c) Similarly, the five-rupees coin will have more mass and therefore more inertia compared to the one-rupee coin.

In summary, without specific information about the masses of the objects in (a), we can conclude that the train in (b) and the five-rupees coin in (c) have more inertia compared to the bicycle and the one-rupee coin, respectively

2. In the following example, try to identify the number of times the velocity of the ball changes: “A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team”. Also identify the agent supplying the force in each case.

Answer: The velocity of the ball changes three times in the given example.

(i) The first change occurs when the first player kicks the ball to another player. The agent supplying the force is the first player's foot.

(ii) The second change happens when the second player kicks the ball towards the goal. The agent supplying the force is the second player's foot.

(iii) The third change takes place when the goalkeeper collects the ball and kicks it towards a player of his own team. The agent supplying the force is the goalkeeper's foot.

---

Posted 4 months ago