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
1
To minimize the force required to open a door, where should the handle be positioned?
Answer:
None of these
The torque required to rotate a door is given by the product of force and the perpendicular distance from the pivot (hinge). To minimize the force needed for a given torque, the distance (lever arm) must be maximized. Therefore, the handle should be placed as far as possible from the hinges, typically at the outer edge of the door.
2
To minimize the force required to open a door, where should the handle be positioned relative to the hinges?
Answer:
away from mid-point opposite to hinges
The torque required to rotate a door is given by the product of force and the perpendicular distance from the axis of rotation (hinges). By placing the handle as far as possible from the hinges, the lever arm is maximized, which minimizes the force needed to produce the necessary torque to open the door.
3
Torque is defined as the rotational or turning effect produced by which of the following?
Answer:
force
Torque, also known as the moment of force, is the physical quantity that measures the tendency of a force to rotate an object about an axis. It is mathematically defined as the cross product of the position vector and the applied force vector. Therefore, torque is fundamentally the turning effect generated by an applied force.
4
What are the dimensional units of the rotational force (torque) that induces rotation in an object?
Answer:
ML2T-2
Torque is defined as the product of force and the perpendicular distance from the axis of rotation. Since force has dimensions of MLT-2 and distance has dimensions of L, the resulting dimension for torque is (MLT-2) * L = ML2T-2. This unit is used to quantify the rotational force in various mechanical systems.
5
How does a central force influence the production of torque on an object?
Answer:
Is unable to produce torque
A central force is defined as a force that acts along the line connecting the center of the force to the object. Since the lever arm (the perpendicular distance from the pivot point to the line of action of the force) is zero, the torque, defined as the cross product of the position vector and the force vector, is necessarily zero.
6
What is the magnitude of the torque produced when a force is applied directly through the center of mass of an object?
Answer:
zero
Torque is defined as the cross product of the position vector and the force vector (τ = r × F). When a force is applied at the center of mass, the lever arm or position vector relative to the pivot point is zero, resulting in zero torque.
7
Which of the following provides a valid definition of torque?
Answer:
All A, B and C are correct
Torque is the rotational force that causes an object to rotate, and it can be defined as the turning effect of force, the cross product of the position vector and force, or the product of the force and moment arm. All three options are correct and describe different aspects of torque, ranging from conceptual definitions to mathematical formulations.
8
How is the equilibrium of a body classified if it does not return to its original position after a slight displacement?
Answer:
unstable equilibrium
A body is in unstable equilibrium if, upon being slightly displaced, the force or torque acting on it tends to move it further away from its original position. In this state, the center of gravity is typically at its highest point.
9
When two children sit on a seesaw and remain perfectly balanced without moving, what is the net torque acting on the system?
Answer:
zero
For a system to be in rotational equilibrium, the sum of all torques acting on it must be zero. If the seesaw is not rotating or swinging, the clockwise torque produced by one child must be exactly balanced by the counter-clockwise torque produced by the other, resulting in a net torque of zero.
10
How is the stability of a racing car improved?
Answer:
lowering their center of gravity
Lowering the center of gravity increases the stability of a vehicle by reducing the tendency to tip over during cornering. A lower center of gravity ensures that the gravitational force acts closer to the ground, requiring a greater lateral force to cause the vehicle to rotate about its outer wheels.