Among the following colours, which is the highest absorbent of heat radiations?
Black colour is the highest absorbent of heat radiations.
No work is said to be done, when an object moves at an angle of ____ with the direction of the force.
Given, W = 0 Work done is given by, W = FScosθ cosθ = 0; θ = 90° Hence, work done is zero.
A girl lifts a doll from the floor and places it on a table. If the weight of the doll is known, then ____ is required to calculate the work done by the girl on the doll.
Given, force, F = mg; Work done is given by the girl, W = FScosθ To find the work done by the girl, displacement is required. The doll is moved from the ground to the top of table. Hence, the height of the table is required to find the work done by the girl on the doll.
In the SI system, the unit of potential energy, PE, is ____.
In the SI system, the unit of potential energy, PE, is joule.
When a body is whirled in a circle, then work done on it by the tension in the string is ____.
Work done is given by, W = FScosθ As, θ = 90° and cos90° = 0 Hence, work done by the tension in the string is zero.
A watch spring in the wounded position has both kinetic as well as potential energies.
Potential energy is stored in the spring by change in configuration of the body.
A solar cell converts?
Solar cells are used to convert solar energy into electrical energy.
When a body is released from a height the kinetic energy of the body is gradually changed into potential energy.
When a body is released from a height the potential energy of the body is gradually changed into kinetic energy. In this case total mechanical energy is conserved or constant. Total energy = KE + PE
Most of the energy we use originally comes from
The energy in biomass, wind, solar energy and fossil fuels originally come from the Sun.
When the pendulum bob is in the mean position, total energy will be minimum.
When the pendulum bob is in the mean position, the total energy will remain unchanged. Total energy is the sum of KE and PE. At mean position, the KE is maximum and PE is zero. Hence, the total energy remains unchanged.
When the force applied and the displacement of the body is inclined at 90°, with each other, the work done is ____.
Work done = FScosθ As, cos90° = 0 Therefore, work done is zero.
Work done by a centripetal force ____.
Work done, W = FScosθ Centripetal force is always perpendicular to the direction of displacement. θ = 90°, cos90° = 0. Hence, work done by the centripetal force is always zero.
kg m2/s2 represents the unit of ____.
Work done, W = FScosθ SI unit of work is N m (or) kg m2/s2 and torque = r × F SI unit of torque is N m (or) kg m2/s2 Hence, work done and torque have same unit.
Which of the following fuel is the least polluting?
The by-product of hydrogen, when used as a fuel and burnt, is water while that of CNG are water and carbon dioxide gas. Water is an absolutely harmless by-product, however, carbon dioxide in the environment causes greenhouse effect leading to global warming. Hence, hydrogen can be called the cleanest fuel.
To describe work done on an object, we require:
To describe work done on an object, we require: The magnitude of the net force acting on the object, its initial position and its final position.
A bird flying in the sky has only kinetic energy.
Flying bird has both velocity as well as altitude so it has both KE and PE.
Work done by the gravitational force on a body is ____.
When a body is carried along the direction of the gravitational force, the work done is positive and vice-versa. When the displacement is made perpendicular to the direction of the gravitational force, the work done is zero. A body is moved from A to B in three different paths in conservative force field. The work done will be maximum when the body is moved along the longest path.
A 1kW hair dryer is used for half an hour. How much energy is used?
1 unit = 1 kWh Energy = power x time = 1kW x 0.5 h = 0.5 units
Complete the sentence, The Sun has been radiating an enormous amount of energy at the present rate for nearly------- years and will continue radiating at that rate for about -------- years more.
The Sun has been radiating an enormous amount of energy at the present rate for nearly 5 billion years and will continue radiating at that rate for about 5 billion years more.
Fuel used in thermal power plants is:
Large amount of fossil fuels are burnt every day in power stations to heat up water to produce steam which further runs the turbine to generate electricity.
A body is moved from A to B in three different paths in conservative force field. The work done will be maximum when the body is moved along the longest path.
Work done by the conservative force does not depend upon the path followed by the body. It depends upon the displacement covered from initial position to final position.
Which of the following is not a constituent of coal gas?
Carbon-di-oxide is not a constituent of coal gas.
When a ball is thrown vertically upwards its velocity keeps on decreasing. What happens to its kinetic energy when it reaches the maximum height?
The kinetic energy becomes zero. According to the law of conservation of energy the kinetic energy is converted into potential energy. Potential energy is maximum at this height.
A constant force applied on the body displaces it through a distance's', so that the angle between force and displacement is 'θ'. Work done will be maximum when ____.
Work done, W = FScosθ work done will be maximum if cosθ = 1 cos0° = 1 Therefore, work done will be maximum when θ = 0°
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