Physics MCQs
Topic Notes: Physics
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
31
Why is it recommended to take smaller steps when walking on ice to prevent slipping?
Answer:
friction of ice is small
Ice provides very low static friction, which is necessary to provide the horizontal force required for walking. By taking smaller steps, the angle of the force exerted by the foot is kept more vertical, reducing the horizontal component of the force that would otherwise exceed the limited frictional force available, thus preventing a slip.
32
What is the specific term for the frictional force that opposes the motion of a body rolling across a surface?
Answer:
rolling friction
Rolling friction, also known as rolling resistance, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. It is generally much weaker than sliding friction because the contact area is smaller and the deformation of the surfaces is minimized, allowing for more efficient movement.
33
What term describes the maximum magnitude of static friction that acts on an object before it begins to slide?
Answer:
limiting friction
Limiting friction is the maximum value of static friction that comes into play when a body is just on the verge of moving over the surface of another body. Once the applied force exceeds this value, the body starts sliding.
34
What is the term for the loss of traction caused by excessive braking that leads to a vehicle sliding?
Answer:
Braking
A skid happens whenever the tires lose their grip on the road. Braking skids occur when the brakes are applied so hard that the front or rear wheels lose traction. This loss of friction between the tire and the road surface prevents the vehicle from responding to steering inputs, leading to an uncontrolled slide.
35
Which physical phenomenon is primarily responsible for the accumulation of static electric charges that can lead to fire or explosion hazards?
Answer:
friction
Triboelectric charging, or friction, occurs when two materials come into contact and are then separated. This process causes a transfer of electrons between surfaces, leading to a build-up of static charge. In industrial environments, this discharge can ignite flammable vapors or dust, posing a significant safety risk.
36
Why is it harder to initiate the movement of a loaded cart compared to maintaining its motion?
Answer:
There is less friction once the cart starts moving
This phenomenon occurs because static friction, which must be overcome to start an object moving, is generally greater than kinetic (or sliding) friction, which acts on an object already in motion. Once the cart is moving, the surfaces are not interlocking as deeply as they were at rest, resulting in less resistance and requiring less force to keep the cart in motion.
37
What is the term for the maximum value of static friction that acts on an object just before it begins to slide?
Answer:
limiting friction
Limiting friction is the maximum value of static friction that comes into play when a body is just on the verge of moving over the surface of another body. Once the applied force exceeds this limiting value, the object begins to move, and kinetic friction takes over.
38
Why is walking on a sandy surface more physically demanding than walking on a concrete surface?
Answer:
the friction between sand and feet is less than that between concrete and feet.
Walking requires static friction between the foot and the ground to provide the necessary traction to push off. On a concrete surface, the high coefficient of friction allows for efficient force transfer. On sand, the particles shift and slide, resulting in lower effective friction, which makes it harder to gain the necessary grip to propel oneself forward.
39
Why must a cyclist continue to pedal while riding a bicycle on a flat surface?
Answer:
friction
A cyclist must continuously apply force by pedaling to counteract the resistive forces acting against the motion, primarily friction between the tires and the road, as well as air resistance. Without this input of energy, these dissipative forces would cause the bicycle to decelerate and eventually stop.
40
What is the primary mechanical purpose of incorporating ball bearings into rotating assemblies like bicycle wheels or scooter axles?
Answer:
Reduce the friction between the wheel and the axle
Ball bearings are designed to facilitate smooth rotation by replacing sliding friction with rolling friction. Because rolling friction is significantly lower than sliding friction, ball bearings minimize energy loss and wear between the rotating wheel and the stationary axle, thereby improving mechanical efficiency.