🔹 Balanced and Unbalanced Forces
Q1. A ball is hanging at rest from the ceiling. Is any force acting on it?
Yes. Gravity pulls it down, and the string pulls it up. These two forces are equal and opposite — so they are balanced.
Q2. Can a body move under balanced forces?
Yes. If it was already moving at constant speed, balanced forces will not stop or accelerate it.
Q3. What change does an unbalanced force bring?
Unbalanced forces cause change in speed, direction, or both — they cause acceleration.
🔹 Newton’s First Law of Motion
Q1. Why is seatbelt important in a moving car?
If the car stops suddenly, the person’s body wants to keep moving forward due to inertia. A seatbelt prevents injury.
Q2. Why does a coin placed on a card fall into the glass when the card is flicked?
Because of inertia. The card moves, but the coin tends to stay at rest and falls straight down.
🔹 Inertia and Mass
Q1. Which has more inertia – a car or a bicycle?
A car has more mass, so it has more inertia. It resists motion changes more than a bicycle.
Q2. Can two objects have the same mass but different inertia?
No. Inertia depends only on mass — more mass means more inertia.
🔹 Newton’s Second Law of Motion
Q1. How does catching a cricket ball slowly reduce pain?
By increasing the time to stop the ball, the force becomes smaller (Impulse = Force × Time).
Q2. Why is a truck harder to accelerate than a car?
It has more mass. So, for the same force, acceleration is less.
🔹 Mathematical Formulation of Second Law
Q1. Write the formula connecting force and momentum.
F = (mv - mu)/t — Force equals change in momentum divided by time.
Q2. What does it mean if F = 0?
It means there is no change in motion. The object moves at constant velocity or stays at rest.
🔹 Newton’s Third Law
Q1. Why does a gun recoil backward?
The bullet moves forward (action), and the gun moves backward with equal momentum (reaction).
Q2. Why can we walk forward?
We push the ground backward, and the ground pushes us forward with equal and opposite force.
🔹 Law of Conservation of Momentum
Q1. Two ice skaters push each other and move in opposite directions. Why?
They both gain momentum, but in opposite directions. Total momentum remains zero as before.
Q2. Why is momentum conserved in absence of external force?
Because only external force can change total momentum of a system.
🔹 Recoil Velocity
Q1. How does mass of a gun affect recoil?
Greater mass means lower recoil velocity because vr = -(m × v) / M
Q2. Can the gun recoil with more speed than the bullet?
No. Since its mass is more, velocity will be less to conserve momentum.
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