Loading PDF...
Chapter Analysis
Intermediate19 pages • EnglishQuick Summary
This chapter on Laws of Motion introduces Newton's three fundamental laws of motion which form the foundation of classical mechanics. It explains the concepts of force, inertia, momentum, and action-reaction pairs, using these to describe the nature of motion. The discussion covers static and kinetic friction, centripetal force, and applications like circular motion and free-body diagrams. The principles of conservation of momentum and different types of forces encountered in physics, such as gravitational, tension, and contact forces, are also covered.
Key Topics
- •Newton's Laws of Motion
- •Friction: Static and Kinetic
- •Centripetal Force and Circular Motion
- •Free-body Diagrams
- •Conservation of Momentum
- •Types of Forces (Gravitational, Tension, Normal, Frictional, etc.)
Learning Objectives
- ✓Understand and apply Newton's three laws of motion.
- ✓Differentiate between static and kinetic friction and their implications.
- ✓Calculate the effects of forces in linear and circular motions.
- ✓Utilize free-body diagrams to analyze mechanical problems.
- ✓Apply the principle of conservation of momentum in collisions.
Questions in Chapter
Give the magnitude and direction of the net force acting on (a) a drop of rain falling down with a constant speed, (b) a cork of mass 10 g floating on water, (c) a kite skillfully held stationary in the sky, (d) a car moving with a constant velocity of 30 km/h on a rough road, (e) a high-speed electron in space far from all material objects, and free of electric and magnetic fields.
Page 69
A pebble of mass 0.05 kg is thrown vertically upwards. Give the direction and magnitude of the net force on the pebble, (a) during its upward motion, (b) during its downward motion, (c) at the highest point where it is momentarily at rest. Do your answers change if the pebble was thrown at an angle of 45° with the horizontal direction? Ignore air resistance.
Page 69
Give the magnitude and direction of the net force acting on a stone of mass 0.1 kg (a) just after it is dropped from the window of a stationary train, (b) just after it is dropped from the window of a train running at a constant velocity of 36 km/h, (c) just after it is dropped from the window of a train accelerating with 1 m s-2, (d) lying on the floor of a train which is accelerating with 1 m s-2, the stone being at rest relative to the train. Neglect air resistance throughout.
Page 69
One end of a string of length l is connected to a particle of mass m and the other to a small peg on a smooth horizontal table. If the particle moves in a circle with speed v the net force on the particle (directed towards the centre) is: (i) T, (ii) lmv2, (iii) 2lmv, (iv) equal to
Page 69
A body of mass 0.40 kg moving initially with a constant speed of 10 m s-1 to the north is subject to a constant force of 8.0 N directed towards the south for 30 s. Take the instant the force is applied to be t = 0, the position of the body at that time to be x = 0, and predict its position at t = –5 s, 25 s, 100 s.
Page 70
Additional Practice Questions
How does Newton's second law of motion explain the acceleration of a car?
mediumAnswer: Newton's second law states that the force acting on an object is equal to the mass of that object multiplied by its acceleration (F = ma). In the case of a car, the engine generates force by burning fuel, which is applied to the car's mass, resulting in acceleration.
Explain the difference between static and kinetic friction with examples.
mediumAnswer: Static friction is the force that keeps an object at rest and prevents it from moving, up to a certain limit, and is generally greater than kinetic friction. For example, static friction keeps a heavy box in place until enough force is applied to move it. Kinetic friction, on the other hand, acts on an object in motion and is usually less than static friction. For instance, once the box starts sliding, kinetic friction is what opposes its movement.
What role does friction play in walking?
easyAnswer: Friction provides the necessary grip between our feet and the ground, allowing us to push off the ground and walk. Without friction, our feet would simply slide back, making it impossible to walk effectively.
What is the principle of conservation of momentum, and how does it apply to collisions?
hardAnswer: The principle of conservation of momentum states that in an isolated system, the total momentum remains constant if no external forces are acting on it. In a collision, the total momentum before the impact is equal to the total momentum after the impact, assuming no external forces like friction or air resistance interfere.
Describe how a free-body diagram can be useful in solving physics problems.
easyAnswer: A free-body diagram helps visualize the forces acting on an object, simplifying complex systems into solvable equations by isolating affecting forces such as gravitational, normal, frictional, and applied forces. This allows for a clear understanding of net forces and accelerations, facilitating problem-solving.