WORK POWER & ENERGY
Q-Why does an athlete run a certain distance before taking a long jump?
A-Running before the jump allows the athlete to build up a significant forward velocity, thereby gaining inertia of motion and linear momentum. This built-up momentum helps carry their body further through the air when they launch off the ground, resulting in a longer jump.
Q-Why are vehicles fitted with shock absorbers (shocks)? Explain using the concept of impulse.
A-When a vehicle hits a bump or pothole, a sharp change in momentum occurs. Shock absorbers are designed to prolong the time duration (t) over which this momentum change takes place. By stretching out the time, the sudden impact force (F) transmitted to the chassis and passengers is greatly reduced, making the ride smoother.
Q-A boxer moves his head backward when a punch is thrown at his face. Explain the physics behind this defensive action.
A-By moving his head backward along with the incoming punch, the boxer extends the time of contact between the glove and his face. Because the time interval (t) required to halt the punch increases, the average impact force (F) of the blow drops, reducing the potential severity of the injury.
Q-State the Law of Conservation of Linear Momentum. Give a real-world example.
A-The Law of Conservation of Linear Momentum states that if no external net force acts on a system of interacting bodies, the total linear momentum of the system remains constant.
Example: Recoil of a gun. Before firing, the total momentum of the gun and bullet is zero. When fired, the bullet flies forward with positive momentum, forcing the gun to move backward with an equal and opposite negative momentum, maintaining a total system momentum of zero.
Q-Can a body have a constant speed but changing linear momentum? Give an example.
A-Yes. Linear momentum (p = mv) is a vector quantity that depends on velocity, which includes both speed and direction. If an object moves in a uniform circular motion, its speed remains completely constant, but its direction changes continuously. Because the velocity’s direction is constantly shifting, its linear momentum is changing at every instant.
Q-Two bodies, X and Y, have equal kinetic energies. If the mass of X is greater than the mass of Y, which body has more linear momentum?
A-The relationship between momentum (p) and kinetic energy (K) is given by p = {2mK}^1/2. Since their kinetic energies (K) are identical, momentum depends directly on the mass (p directly propotional to m). Because body X has a larger mass, body X will have greater linear momentum.
Q-Name the primary energy transformations that occur in the following devices.
A-Electric Roller/Heater: Electrical energy transforms into Heat energy.
Solar Cell: Light (solar) energy transforms into Electrical energy.
Microphone: Sound energy transforms into Electrical energy.
Loudspeaker: Electrical energy transforms into Sound energy.
Q-Differentiate between gravitational potential energy and elastic potential energy with examples.
A-Gravitational Potential Energy: Energy stored in an object due to its position relative to the ground (e.g., water stored upstream in a mountain dam).
Elastic Potential Energy: Energy stored in an object due to a change in its shape, compression, or stretching (e.g., a stretched rubber band or a compressed toy spring).
Q-What is mechanical energy? Name its two types and give an example of an object that possesses both simultaneously.
A-Mechanical energy is the total energy possessed by an object due to its motion or its position/configuration. Its two types are Kinetic Energy and Potential Energy.
Example: A flying airplane or a bird gliding in the sky possesses both. It has kinetic energy because it is moving forward, and potential energy because it is at a height above the ground.
Q-State the Law of Conservation of Energy and explain how it applies to a freely falling body.
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A-The Law of Conservation of Energy states that energy can neither be created nor destroyed; it can only be transformed from one form to another. When an object is dropped from a height, its initial energy is entirely Potential Energy (PE). As it falls, its height decreases (PE drops) and its speed increases (Kinetic Energy, KE, increases). At any point during the fall, the sum of PE and KE remains constant. Just before hitting the ground, all PE is fully converted into KE.
Q-A satellite moves in a perfectly circular orbit around the Earth. Why is the work done by the Earth’s gravitational pull on the satellite zero?
A-At every point along the circular path, the gravitational force acts radially inward toward the center of the Earth, while the satellite’s instantaneous displacement is tangential to the orbit. Because the force and displacement vectors are always perpendicular to each other. in this case W= F.dcos90. = 0
Q-A coolie stands completely still for 30 minutes with a massive load of 50 kg on his head. How much physical work is done according to physics?
A-According to physics, the work done is zero. Work requires a displacement to take place (W = F . d). Because the coolie is standing completely still, the displacement (d) is zero, meaning no mechanical work is performed on the load.