Work And Energy (Test - 2) - Class 9 Science, 21-02-2018 - Class 9 MCQ

With increase in temperature, the kinetic energy of molecules increases and start vibrating with faster speed. Potential energy depends on height so, when a body falls towards the surface of the earth, its P.E decreases.

One kg of butter provides more energy to human body after digestion in comparison to 1 kg of rice, potatoes and salad.

Power of bulb = 150w, work done = 3000 joule, time taken= work done/power = 3000/150 = 20 s.

Kinetic energy of a body is K.E =1/2 mv². Kinetic energy depends upon mass of the body and velocity. Since mass and velocity never be negative, kinetic energy is always positive.

Two bodies having equal kinetic energy may or may not have equal momentum. The work done by centripetal force is always greater than zero. Centripetal force is present in the body moving on circular path.

Initial velocity (u) = 30 km/h = 30×5/18 = 25/3 m/s. final velocity (v) =60 = 50/3 m/s. mass = 1500 kg. work done = change in kinetic energy  

 

The momentum of a body is equal to product of mass and velocity. If momentum of a body is double, the kinetic energy is becomes four times as K.E =  1/2 mv²

To match the given scenarios with the correct response, we need to understand the concept of potential energy and kinetic energy.
Potential energy:
Potential energy is the energy possessed by an object due to its position or state.
Kinetic energy:
Kinetic energy is the energy possessed by an object due to its motion.
Now, let's match the scenarios with the correct response:
1. Bullet fired from gun:
- The bullet is initially at rest in the gun, so it has potential energy.
- As it is fired, the bullet starts moving and gains kinetic energy.
- Response: (1) - C (Potential energy)
2. A flying bird:
- The bird is in motion, so it has kinetic energy.
- Response: (2) - B (Kinetic energy)
3. In a falling stone:
- The stone is initially at a higher position, so it has potential energy.
- As it falls, its potential energy decreases and gets converted into kinetic energy.
- Response: (3) - A (Potential energy changes to kinetic energy)
4. Water at dam:
- The water is stored at a higher position in the dam, so it has potential energy.
- When the water is released and flows down, its potential energy decreases and it gains kinetic energy.
- Response: (4) - D (Kinetic & Potential energy)
Therefore, the correct match is:
Answer: a. (1-C, 2-B, 3-A, 4-D)

Explanation:
The correct matching of the terms with their definitions is as follows:
(1) Kinetic energy - Energy due to motion
(2) Potential energy - Energy due to position
(3) Work - Force displaces an object in the direction of force
(4) Power - The rate of doing work
Summary:
To summarize, the correct matching is:
1-A: Kinetic energy - Energy due to motion
2-C: Potential energy - Energy due to position
3-B: Work - Force displaces an object in the direction of force
4-D: Power - The rate of doing work
Therefore, the correct answer is B: 1-D, 2-A, 3-C, 4-B.

Force is the product of mass and acceleration due to gravity. Mass = 2m and acceleration due to gravity =g m/s². Force = 2m×g= 2mg

In a watch potential energy of wound of spring is converted into kinetic energy of hands of watch.

Explanation:

When an object starts to fall freely, the following changes occur:

• Kinetic Energy: The object gains kinetic energy as it falls due to its motion. The potential energy is converted into kinetic energy.


• Potential Energy: The object loses potential energy as it falls. The height from which it falls decreases, resulting in a decrease in potential energy.

Based on the above information, we can conclude that:

• Statement A: The potential energy is increased and kinetic energy is decreased. Correct


• Statement B: The kinetic energy is increased and potential energy is decreased. Correct


• Statement C: Potential energy remains unchanged. Incorrect


• Statement D: Kinetic energy remains unchanged. Incorrect

Therefore, the correct answer is option C: (a), (c) and (d) are correct.

To match the given options with the correct responses, we need to understand the concepts of velocity effects, maximum work done, work done being zero, and work done when a force acts obliquely.
Velocity Effects:
- Velocity effects refer to the influence of velocity on the work done. It can determine the amount of work done in a given situation.
Maximum Work Done:
- Maximum work done occurs when the force and displacement are in the same direction, resulting in the highest amount of work done.
Work Done is Zero:
- Work done is zero when the force and displacement are perpendicular to each other. In such cases, the force does not contribute to the displacement.
Work Done when Force Acts Obliquely:
- When the force acts obliquely, only the component of force in the direction of displacement contributes to the work done. The work done can be calculated using the formula: work done = force × displacement × cosθ, where θ is the angle between the force and displacement vectors.
Now, let's match the given options with the correct responses:
(A) Energy - Velocity effects
(B) 90° - Work done is zero
(C) 0° - Maximum work done
(D) F × S × cosθ - Work done, when force acts obliquely
Therefore, the correct matching is:
- 1-A (Velocity effects)
- 2-C (Maximum work done)
- 3-B (Work done is zero)
- 4-D (Work done when force acts obliquely)
Hence, the correct answer is option C.

Mass = 20 kg, height = 20×20/100 m= 4m, time taken = 20 s. power = work done/ time, power = mgh/t. = 20×10×4/20watt = 40 w.

When a body is thrown vertically upwards, during its upward movement the potential energy is increase due to increase in height and kinetic energy decreases due to decrease in velocity.

When an object falls from a height h, it possesses both potential energy and kinetic energy. As the object falls to a height of h/2, the following changes occur:
Half potential energy:
- The potential energy of an object at height h is given by mgh, where m is the mass of the object, g is the acceleration due to gravity, and h is the height.
- When the object falls to a height of h/2, the potential energy becomes mgh/2.
- Therefore, the object possesses half of its initial potential energy at this point.
Only kinetic energy:
- The kinetic energy of an object is given by (1/2)mv^2, where m is the mass of the object and v is its velocity.
- As the object falls, its potential energy is converted into kinetic energy.
- At a height of h/2, the object has lost half of its initial potential energy and gained an equal amount of kinetic energy.
- Therefore, at this point, the object only possesses kinetic energy.
Therefore, the correct answer is option C: Only kinetic energy.

The correct matching of the given statements is as follows:
(1) Law of conservation of energy - (B) Energy neither be created nor be destroyed
(2) Stretched rubber band possess - (D) Potential energy
(3) At mean position pendulum attains maximum - (A) kinetic energy
(4) Various energy forms are - (C) Interconvertible
Explanation:
Law of conservation of energy:
- The law of conservation of energy states that energy cannot be created or destroyed, it can only be transferred or converted from one form to another.
- This means that the total energy of a closed system remains constant over time.
Stretched rubber band possess:
- When a rubber band is stretched, it gains potential energy.
- This potential energy is stored in the rubber band and can be released when the band is allowed to snap back to its original shape.
At mean position pendulum attains maximum:
- In a pendulum, the mean position is the equilibrium position where the pendulum is at rest.
- At this position, the pendulum has the maximum potential energy.
- As the pendulum swings away from the mean position, the potential energy is converted into kinetic energy.
Various energy forms are:
- Energy exists in various forms such as kinetic energy, potential energy, thermal energy, electrical energy, etc.
- These energy forms are interconvertible, meaning they can be transformed from one form to another.
- For example, electrical energy can be converted into light energy in a light bulb, and chemical energy can be converted into mechanical energy in a car engine.
Conclusion:
- The correct matching of the statements is A: 1-B, 2-D, 3-A, 4-C.

Work done = F×S×Cosϕ, Cos 90⁰= 0, so, Q =45⁰.

The point of maximum K.E in case of oscillating pendulum is at mean position. As K.E depends upon velocity and mass. Maximum velocity is at mean position of pendulum.

Our hands become warm when rubbed against each other. This is because kinetic energy is converted into heat energy due to friction between palms.

To match the given statements with the correct responses, let's analyze each statement and its corresponding options:
Statement 1: Nm is also called
- Option A: Potential energy is equal to kinetic energy
- Option B: Work done
- Option C: No work done
- Option D: Erg
Statement 2: Free fall
- Option A: Potential energy is equal to kinetic energy
- Option B: Work done
- Option C: No work done
- Option D: Erg
Statement 3: A donkey is working with a load on its back
- Option A: Potential energy is equal to kinetic energy
- Option B: Work done
- Option C: No work done
- Option D: Erg
Statement 4: An engine is pulling a train
- Option A: Potential energy is equal to kinetic energy
- Option B: Work done
- Option C: No work done
- Option D: Erg
Now, let's match each statement with the correct response:
Statement 1: Nm is also called
- Option A: Potential energy is equal to kinetic energy (Incorrect)
- Option B: Work done (Incorrect)
- Option C: No work done (Correct)
- Option D: Erg (Incorrect)
Statement 2: Free fall
- Option A: Potential energy is equal to kinetic energy (Incorrect)
- Option B: Work done (Correct)
- Option C: No work done (Incorrect)
- Option D: Erg (Incorrect)
Statement 3: A donkey is working with a load on its back
- Option A: Potential energy is equal to kinetic energy (Incorrect)
- Option B: Work done (Incorrect)
- Option C: No work done (Correct)
- Option D: Erg (Incorrect)
Statement 4: An engine is pulling a train
- Option A: Potential energy is equal to kinetic energy (Correct)
- Option B: Work done (Incorrect)
- Option C: No work done (Incorrect)
- Option D: Erg (Incorrect)
Based on the analysis, the correct matching of the statements with their responses is:
A: 1-C, 2-B, 3-D, 4-A
Therefore, the correct answer is option B: 1-C, 2-B, 3-D, 4-A.

Work done/time = power, here work done is same. Power of person P =W/t_p.  Power of person Q =W/tq. The  ratio of power = W/tp: W/tq= tq/tp

In the pendulum potential energy is converted into kinetic energy when swing towards mean position. In explosion chemical energy is converted into heat and sound energy. In torch, chemical energy is converted into electrical energy.

The head of a nail hammered into the wooden plank becomes hot because some part of kinetic energy is converted into heat energy.

Explanation:
The correct statement is: C: (c) and (d) are correct.
- A: A bird sitting on a tree possesses potential energy only. This is because potential energy is the energy that an object possesses due to its position or condition. When a bird is sitting on a tree, it has potential energy due to its height and its ability to fall or move.
- B: A stationary object may have energy. This is true because even though the object is not moving, it still possesses potential energy. For example, a book on a shelf has potential energy due to its position above the ground.
- C: A flying bird has kinetic energy only. This statement is incorrect. When a bird is flying, it possesses both kinetic energy and potential energy. Its movement through the air gives it kinetic energy, while its height above the ground gives it potential energy.
- D: An airplane running on the runway possesses both kinetic and potential energy. This statement is correct. When an airplane is running on the runway, it has kinetic energy due to its motion, and potential energy due to its height above the ground.
Therefore, the incorrect statement is C: A flying bird has kinetic energy only.

Work is said to be done when there is a displacement of the body with respect to moving body. No work is done when a camel is carrying a load on its back. But work is done when a sailboat is moving due to wind energy.

Gravitational potential energy depends upon mass, height and acceleration due to gravity. P.E = mgh.

Lever is a simple machine that makes the work easier. There is no energy conversion in lever. Muscular energy is present in the muscle of animals. So, above statement is false.

Answer:
To determine which of the following is not a vector quantity, let's examine the properties of each option:
A. Energy:
- Energy is a scalar quantity, not a vector quantity.
- It is measured in joules (J) and represents the capacity to do work or produce heat.
- Energy does not have a direction associated with it.
B. Kinetic energy:
- Kinetic energy is a scalar quantity, not a vector quantity.
- It is defined as the energy of an object due to its motion.
- Kinetic energy depends on the mass and speed of an object, but not its direction.
C. Work done:
- Work done is a scalar quantity, not a vector quantity.
- It is defined as the product of the force applied to an object and the displacement of the object in the direction of the force.
- Work done depends on the magnitude of the force and the distance moved, but not the direction.
D. Power:
- Power is a scalar quantity, not a vector quantity.
- It is defined as the rate at which work is done or energy is transferred.
- Power is measured in watts (W) and depends on the amount of work done or energy transferred per unit time.
Therefore, the answer is A. Energy because it is not a vector quantity.