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
11
What occurs physically when a projectile is discharged from a firearm?
Answer:
The gun recoils with the same momentum as the bullet
According to Newton's Third Law of Motion and the Law of Conservation of Momentum, when a gun exerts a forward force on a bullet, the bullet exerts an equal and opposite force on the gun. Consequently, the gun experiences a backward velocity known as recoil. Since the system is isolated, the total momentum remains zero, meaning the magnitude of the gun's momentum equals the magnitude of the bullet's momentum.
12
What is the effect of a motorcycle safety helmet on the impulse experienced during a collision?
Answer:
decreases the impulse
Impulse is defined as the change in momentum, which is equal to the average force multiplied by the time interval of the impact. A helmet increases the time duration of the collision, which effectively reduces the average force exerted on the head. While the total change in momentum (impulse) is technically the same, the helmet reduces the peak force, often described in this context as reducing the impulsive impact.
13
A 100g cricket ball moving at 30 m/s is brought to rest in 0.05 seconds. Calculate the average force exerted by the player.
Answer:
-60 N
Using Newton's Second Law in terms of momentum: F = Δp / Δt = m(v - u) / Δt. Given m = 0.1 kg, v = 0, u = 30 m/s, and Δt = 0.05 s, the force is 0.1 * (0 - 30) / 0.05 = -3 / 0.05 = -60 N. The negative sign indicates the force opposes the initial motion.
14
Which physical principle explains the operation of a jet engine?
Answer:
conservation of linear momentum
A jet engine operates by expelling high-velocity exhaust gases backward. According to the law of conservation of linear momentum, the momentum gained by the exhaust gases in one direction must be balanced by an equal and opposite momentum gained by the engine, creating forward thrust.
15
What is the linear momentum of an object with a mass of 14 kg moving at a velocity of 28 m/s?
Answer:
392 kg-m/s
Linear momentum (p) is the product of an object's mass (m) and its velocity (v), expressed as p = m * v. By multiplying 14 kg by 28 m/s, we obtain 392 kg·m/s, which represents the total momentum of the object.
16
When two eggs are dropped from the same height, one onto a hard floor and one onto a soft pillow, which of the following is NOT a possible outcome?
Answer:
Both eggs will break
The impulse (change in momentum) is the same for both eggs. Impulse = Force × time. The pillow increases the impact time, significantly reducing the peak force exerted on the egg, preventing it from breaking. The floor results in a very short impact time, leading to a large force that breaks the egg. Option B is unlikely as the pillow is designed to prevent breakage.
17
Which physical properties determine the momentum of a moving object?
Answer:
both mass and velocity of the body
Linear momentum is a fundamental vector quantity in classical mechanics defined as the product of an object's mass and its velocity (p = mv). It quantifies the 'quantity of motion' an object possesses. Therefore, both the mass of the object and its velocity are essential factors in determining its total momentum.
18
The rate of change of linear momentum of an object is equivalent to which physical quantity?
Answer:
force
Newton's Second Law of Motion states that the net force acting on an object is directly proportional to the rate of change of its momentum. Mathematically, F = dp/dt, where p is momentum and t is time. Therefore, the rate of change of momentum is exactly equal to the resultant force applied to the body.
19
How does a motorcycle safety helmet function to protect the wearer during a collision?
Answer:
impulse
A safety helmet is designed to increase the duration of the impact during a collision. According to the impulse-momentum theorem, impulse is the product of force and time. By extending the time over which the change in momentum occurs, the helmet reduces the average impact force exerted on the head, thereby minimizing the risk of injury.
20
A 20g bullet is fired from a 3 kg pistol at 150 m/s. What is the recoil velocity of the pistol?
Answer:
-1.0ms-1
Using the law of conservation of momentum: m1*v1 + m2*v2 = 0. Converting 20g to 0.02kg: (0.02 * 150) + (3 * V) = 0. Thus, 3 + 3V = 0, which gives V = -1.0 m/s. The negative sign indicates the direction of recoil is opposite to the bullet's motion.