1.
A man is carrying the heavy luggage from one platform to the other of a Railway station but still according to the logic of science his work done is said to be zero. Can you opt-out of the correct reason?
Correct Answer
B. The force is acting perpendicular to the direction of displacement of luggage
Explanation
The correct reason is that the force is acting perpendicular to the direction of displacement of the luggage. According to the laws of physics, work is defined as the product of force and displacement, multiplied by the cosine of the angle between them. In this case, since the force is acting perpendicular to the direction of displacement, the angle between them is 90 degrees and the cosine of 90 degrees is zero. Therefore, the work done is zero.
2.
When a body like the earth is moving in a circular path the work done in that case is zero because:
Correct Answer
B. Centripetal force acts along the radius of circular path
Explanation
When a body is moving in a circular path, the centripetal force is responsible for keeping the body in that path. The centripetal force always acts towards the center of the circle, along the radius. Since work is defined as the force applied in the direction of motion, and the centripetal force is perpendicular to the direction of motion, no work is done. Therefore, the work done in this case is zero.
3.
A car is accelerated on a leveled road and attains a velocity 4 times of its initial velocity. In this process, the kinetic energy of the car.
Correct Answer
D. Becomes 16 times to that of the initial
Explanation
When a car is accelerated on a leveled road, its velocity increases. Kinetic energy is directly proportional to the square of the velocity. Since the car's velocity becomes 4 times its initial velocity, the kinetic energy will become 16 times the initial kinetic energy. This is because 4 squared is equal to 16. Therefore, the correct answer is that the kinetic energy becomes 16 times that of the initial kinetic energy.
4.
The momentum of a bullet of mass 20 g fired from a gun is 10 kg.m/s. The kinetic energy of this bullet in kJ will be:
Correct Answer
B. 2.5
Explanation
The kinetic energy of an object can be calculated using the formula KE = (1/2)mv^2, where m is the mass of the object and v is its velocity. In this case, the mass of the bullet is given as 20 g, which is equivalent to 0.02 kg. The momentum of the bullet is given as 10 kg.m/s. Since momentum is defined as p = mv, we can rearrange the equation to solve for velocity: v = p/m. Substituting the given values, we get v = 10/0.02 = 500 m/s. Plugging this value into the kinetic energy formula, we find KE = (1/2)(0.02 kg)(500 m/s)^2 = 2.5 kJ. Therefore, the correct answer is 2.5.
5.
You would have observed a runner who possesses only kinetic energy due to his motion. Can you guess which form of energy does a flying bird have?
Correct Answer
C. Both kinetic and potential energy
Explanation
A flying bird possesses both kinetic and potential energy. Kinetic energy is the energy of motion, which the bird has as it moves through the air. Potential energy is the energy that an object has due to its position or height above the ground. When a bird is flying, it has potential energy due to its height in the air, and it also has kinetic energy due to its motion. Therefore, the correct answer is both kinetic and potential energy.
6.
Which one of the following is not the unit of energy?
Correct Answer
D. Newton meter
Explanation
Newton meter is not a unit of energy. It is a unit of work or torque. Energy is typically measured in units such as kilowatt, kilowatt hour, and joule. Newton meter, on the other hand, is a unit that measures the amount of work done or torque applied.
7.
In the dams, water is stored in the high reservoirs and then made to fall down. This falling water then rotates the turbines to generate electricity. In this energy conversion process can you tell the initial and final energies respectively?
Correct Answer
A. Kinetic energy and electrical energy
Explanation
The initial energy in the energy conversion process is potential energy, as the water is stored in high reservoirs. As the water falls down, it gains kinetic energy. This kinetic energy is then used to rotate the turbines, which in turn generate electrical energy. Therefore, the final energies in this process are kinetic energy and electrical energy.
8.
A man of mass 50 kg jumps to a height of 1 m. His potential energy at the highest point is (g = 10 m/s^{2}):
Correct Answer
B. 500 J
Explanation
The potential energy of an object at a certain height is given by the formula PE = mgh, where m is the mass of the object, g is the acceleration due to gravity, and h is the height. In this case, the mass of the man is 50 kg, the acceleration due to gravity is 10 m/s^2, and the height is 1 m. Plugging these values into the formula, we get PE = (50 kg)(10 m/s^2)(1 m) = 500 J.
9.
The type of energy possessed by a simple pendulum, when it is at the mean position is:
Correct Answer
A. Kinetic energy
Explanation
When a simple pendulum is at the mean position (equilibrium position), it is momentarily at rest before it starts swinging back and forth. At this point, the pendulum has zero potential energy because it is at its lowest point in the swing. However, it still possesses kinetic energy because it has velocity due to its previous motion. Therefore, the correct answer is kinetic energy.
10.
A body is falling from a height h. After it has fallen to a height of h/2, it will possess:
Correct Answer
C. Only potential energy
Explanation
When a body is falling from a height, its potential energy is gradually converted into kinetic energy. As the body falls to a height of h/2, it has not yet reached the ground, so it still possesses potential energy. At this point, all of its initial potential energy has been converted into kinetic energy, and it has not gained any additional kinetic energy. Therefore, the correct answer is that it possesses only potential energy.
11.
Two objects of masses 1 x 10^{-3} kg and 4 x 10^{-3} kg have equal momentum. What is the ratio of their kinetic energies?
Correct Answer
B. 4:1
Explanation
The ratio of the kinetic energies of two objects is equal to the ratio of their masses. In this case, the masses of the two objects are 1 x 10^-3 kg and 4 x 10^-3 kg. Therefore, the ratio of their kinetic energies is 1:4.
12.
The work done on an object does not depend upon the:
Correct Answer
C. Initial velocity of the object
Explanation
The work done on an object is defined as the product of the force applied on the object and the displacement of the object in the direction of the force. The angle between the force and displacement affects the magnitude of the work done, as it determines how much of the force is actually contributing to the displacement. The force applied and the displacement are both crucial factors in determining the work done. However, the initial velocity of the object does not affect the work done, as work is only concerned with the force and displacement during the time the force is being applied. The initial velocity does not play a role in determining the work done.
13.
An iron sphere of mass 10 kg has the same diameter as an aluminum sphere of mass 3.5 kg. Both spheres are dropped simultaneously from a tower. When they are 10 m above the ground, they have the same:
Correct Answer
C. Acceleration
Explanation
Since both spheres are dropped simultaneously from the same height, they experience the same gravitational acceleration. The acceleration due to gravity is independent of the mass or material of the object. Therefore, both spheres will have the same acceleration when they are 10 m above the ground.
14.
A microphone converts:
Correct Answer
B. Sound energy into electrical energy in public address system.
Explanation
A microphone is a device that converts sound energy into electrical energy in a public address system. When sound waves enter the microphone, they cause a diaphragm or a similar element to vibrate. These vibrations are then converted into electrical signals through the use of a transducer. These electrical signals can then be amplified and transmitted through a public address system, allowing the sound to be heard by a large audience. This process is essential for capturing and amplifying sound in public speaking events, concerts, and other similar settings.
15.
Which of the following energy change involves frictional force?
a) Potential energy to sound energy
b) Chemical energy to heat energy
c) Kinetic energy to heat energy
d) Chemical energy to heat energy
Choose the correct option among the following:
Correct Answer
D. Only c
Explanation
The correct answer is "Only c". This is because the energy change from kinetic energy to heat energy involves the frictional force. When an object is in motion, it possesses kinetic energy. When this object comes into contact with a surface or another object, the frictional force between them causes the kinetic energy to be converted into heat energy. Therefore, option c is the correct answer as it describes the energy change involving frictional force.