Important Diagrams: Force and Laws of Motion | Science Class 9 PDF Download

Q1: Answer the following questions based on the diagram given below:

(i) What is Newton's first law of motion?
Ans: Newton's first law of motion states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external unbalanced force.

(ii) In the given experiment, what happens to the ball when no external force is applied?
Ans: When no external force is applied, the ball remains at rest or continues moving at a constant speed in a straight line.

(iii) What happens to the ball when a gentle push is given to it in the experiment?
Ans: When a gentle push is given to the ball, it starts moving in the direction of the push. Once the push is removed, it continues moving at a constant speed in a straight line due to inertia.

(iv) How does Newton's first law of motion explain the ball's behavior in this experiment?
Ans: Newton's first law of motion explains that the ball remains at rest or in uniform motion unless an unbalanced force is applied. The initial rest or motion is due to the ball's inertia, and the gentle push applies an unbalanced force, causing a change in its state of motion.

(v) What is inertia, and how is it related to Newton's first law of motion?
Ans: Inertia is an inherent property of matter that resists any change in its state of motion. It is related to Newton's first law of motion as it describes the tendency of an object to remain at rest or in uniform motion unless acted upon by an external unbalanced force, in accordance with the law.

Q2: Answer the following questions based on the diagram given below:

(i) What happens to the coin when the card is flicked with a sharp horizontal motion?
Ans: When the card is flicked horizontally, the coin falls vertically into the glass tumbler due to its inertia.

(ii) Why does the coin fall into the glass tumbler when the card is flicked?
Ans: The coin falls into the tumbler because of its inertia. The inertia of the coin tries to maintain its state of rest even when the card is moving away, causing the coin to drop into the tumbler.

(iii) What effect does the sharp flicking of the card have on the coin's motion?
Ans: The sharp flicking of the card imparts horizontal motion to the card and the coin. The coin's inertia resists this change in motion, causing it to fall into the tumbler vertically.

(iv) How does inertia play a role in this experiment?
Ans: Inertia is the property of an object to resist changes in its state of motion. In this experiment, the coin's inertia resists the horizontal motion imparted by flicking the card, causing the coin to fall vertically due to gravity.

(v) What role does the glass tumbler play in this experiment?
Ans: The glass tumbler acts as a container to receive the coin when it falls. The coin's vertical motion due to inertia and gravity is guided by the presence of the tumbler, allowing the coin to safely fall into it.

Q3: Answer the following questions based on the diagram given below:

(i) How does the fielder's action of gradually pulling his hands affect the ball's momentum?
Ans: The fielder's action of gradually pulling his hands reduces the rate of change of momentum of the ball, lessening the force exerted on the ball and allowing for a safe catch.

(ii) In the experiment, what is the significance of reducing the rate of change of momentum of the ball?
Ans: By reducing the rate of change of momentum, the fielder decreases the force applied on the ball, minimizing the impact and making it easier to catch without hurting the hands.

(iii) What would happen if the fielder abruptly stopped the ball instead of pulling hands gradually?
Ans: If the fielder abruptly stopped the ball, it would experience a high rate of change of momentum, resulting in a larger force on the ball, potentially causing injury to the hands.

(iv) How does the experiment demonstrate the second law of motion?
Ans: The experiment illustrates the second law of motion by showing that the rate of change of momentum (controlled by how the fielder pulls his hands) is proportional to the force exerted on the ball during the catch.

(v) How does the second law of motion help us understand the physics behind catching a moving ball?
Ans: The second law of motion helps us understand that applying a force (pulling hands gradually) over time reduces the momentum change of the ball, making it easier to catch by minimizing the force required for deceleration.

Q4: Answer the following questions based on the diagram given below:
(i) What is depicted in the experiment regarding the gun and the bullet?
Ans: The experiment demonstrates the application of the third law of motion, showing the recoil of a gun when a bullet is fired.

(ii) Explain the concept of action and reaction forces using this experiment.
Ans: The action force is the forward force exerted on the bullet when the gun is fired, and the reaction force is the equal and opposite force exerted on the gun, causing its recoil.

(iii) Why does the gun recoil when the bullet is fired?
Ans: The gun recoils due to the reaction force exerted by the bullet in the opposite direction to maintain the overall momentum at zero, following the third law of motion.

(iv) How does the mass of the gun and bullet affect their respective accelerations in this experiment?
Ans: The gun's greater mass results in a smaller acceleration compared to the bullet, as acceleration is inversely proportional to mass, following the second law of motion.

(v) Explain another real-life scenario where the third law of motion is illustrated, as mentioned in the text.
Ans: The scenario of a sailor jumping out of a rowing boat is an example where the sailor's forward jump leads to a reaction force pushing the boat backward, showcasing the third law of motion.