Test: Energy - Class 8 MCQ

As an object falls, its gravitational potential energy decreases and is converted into kinetic energy. This transformation is an application of the conservation of mechanical energy, which states that the total energy in a closed system remains constant unless acted upon by external forces.

During a transformation process, energy is conserved but may change from one form to another. This principle is fundamental in physics and helps explain various natural phenomena and technological applications, such as energy generation and consumption.

The formula for kinetic energy is K.E. = ½ m v², where m is the mass of the object and v is its velocity. This formula highlights that kinetic energy increases with the square of the speed, demonstrating how rapidly moving objects have significantly more energy than those moving slowly.

In a solar cell, light energy from the sun is converted into electrical energy. This process involves the absorption of photons by the solar cell material, which generates an electric current. This transformation is essential for harnessing solar energy for various applications, including powering homes and devices.

A stretched bowstring possesses potential energy because work has been done to stretch it. This stored potential energy is converted into kinetic energy when the bowstring is released, propelling the arrow forward. This example illustrates how potential energy can be transformed into kinetic energy.

Gravitational potential energy is the energy stored in an object due to its height above the ground. This energy is determined by the formula P.E. = m × g × h, where m is the mass, g is the acceleration due to gravity, and h is the height. This form of energy is crucial because it can be converted into kinetic energy when the object falls.

The S.I. unit of power is the watt (W), which is equivalent to one joule per second. This unit measures how much work is done or energy is transferred in a certain amount of time, making it a key concept in both physics and engineering.

In scientific terms, work is defined as being done only when a force causes a body to change its position or move. If no movement occurs, such as when lifting a box without moving it, no work is considered to be done. This distinction is crucial in physics, as it separates the common use of the word from its precise scientific meaning.

The amount of work done is determined by two factors: the magnitude of the force applied and the distance moved in the direction of that force. This relationship is mathematically expressed as Work = Force × Distance, making it clear that both force strength and movement distance are essential for calculating work.

The color of the object does not affect its kinetic energy. Kinetic energy is solely dependent on the mass and speed of the object, as described by the formula K.E. = ½ m v². This means that changes in color or appearance do not influence the energy associated with its motion.

Mechanical energy is defined as the sum of potential energy and kinetic energy in a system. It represents the total energy associated with the motion and position of an object, making it a crucial concept in understanding energy dynamics in physical systems.

The potential energy given to the box depends on its mass and the height to which it is lifted. The formula for gravitational potential energy (P.E. = m × g × h) indicates that both the mass of the object and its height above the ground are crucial for determining the energy stored as potential energy.

Increasing the speed of an object results in an increase in kinetic energy proportional to the square of the speed. This means that if the speed doubles, the kinetic energy increases by a factor of four, illustrating the significant impact speed has on kinetic energy.

Power is defined as the rate of doing work, expressed mathematically as Power = Work done / Time taken. This means that a higher power output indicates that work is being completed more quickly, which is important in various applications, from machinery to human effort.

The relationship is such that work is the product of power and time. This can be expressed in the formula Work = Power × Time. This means that for a given power output, the amount of work done increases with the amount of time the power is applied.

Water stored in a dam primarily represents potential energy due to its height above the ground. This potential energy can be converted to kinetic energy when the water is released and allowed to flow down through turbines, generating electricity. This principle is widely used in hydroelectric power generation.

The work done on a body is stored as energy within that body. This concept illustrates the fundamental principle that energy is the capacity to do work, meaning that work and energy are intrinsically linked, with energy being the result of work applied.

One form of energy can indeed be changed into another useful form. For example, mechanical energy can be converted into electrical energy in generators, and electrical energy can be transformed into heat energy in appliances. This versatility of energy forms is fundamental in various technologies and natural processes.

Kinetic energy depends on both the mass of an object and its speed, as described by the formula K.E. = ½ m v². This means that if either the mass or speed of an object increases, its kinetic energy also increases, demonstrating the relationship between motion and energy.

The S.I. unit of work is the joule (symbol J). One joule is defined as the work done when a force of one newton moves an object one meter in the direction of the force. This unit is named after the physicist James Prescott Joule, who contributed significantly to the understanding of energy and work.