Science M.C.Q. [1 M]

1. True

Explanation:

Flowing water possess kinetic energy which is used to do work.

4. Joules

1. No, as machines require a constant input of energy in order to work

1. Kinetic energy

Explanation:

A moving car possesses mechanical energy due to its motion (kinetic energy). A moving baseball possesses mechanical energy due to both its high speed (kinetic energy) and its vertical position above the ground (gravitational potential energy).

3. Force

Explanation:

Kinetic energy is the energy possessed by the body by virtue of its motion and potential energy is the energy possessed by the virtue of its position and shape. Energy is required to do work. 

Hence work, kinetic energy, potential energy all can be measured using same unit, i.e joule. 

So, force is the physical quantity here which is different from others as given by product of mass and acceleration. S.I unit of force is N (newton).

2. Kinetic energy

Explanation:

The energy possessed by the virtue of motion of any object is called kinetic energy.Hence while running the energy possessed by the person is kinetic energy.

2. Maximum

Explanation:

According to the law of conservation of energy its kinetic energy is getting converted in to potential energy because of gain in height. So, if the velocity of a ball goes on decreasing when it is thrown vertically upwards. When its velocity becomes zero, its potential energy becomes maximum.

2. 10kg

Explanation:

We know that , P.E = mgh So, It is directly proportional to height and mass.

Since both the weights are at the same height, so the weight with a larger mass will have more potential energy. 

Since 10kg object has a larger mass than a 5kg, so, the potential energy of a 10kg mass will be greater.

3. K E. is increased to four times

2. 150 Joules

1. 64J

1. Gravitational potential energy

Explanation:

A fruit, hanging from the top branch of a tree, is at rest at a certain height from the earth"s surface. 

So, it possesses gravitational potential energy.

2. Remains constant

Explanation:

Since the ball is in free-fall, the only force acting on it is gravity. Therefore, we can use the principle of conservation of mechanical energy - initially the ball has potential energy and no kinetic energy. As it falls, its total energy (the sum of the KE and the PE) remains constant and equal to its initial PE. when reaches the ground there is no PE only KE I.E., Equal to initial PE

4. Both K.E. and P.E

Explanation:

A ball rolling down a hill has both Kinetic and potential energy. Kinetic energy is due to motion. So if the ball is rolling down it has kinetic energy. Potential energy is the stored energy which is waiting to be used. If the ball is at a greater height it will have more potential energy. So when the body starts rolling the stored potential energy gets converted into kinetic energy which causes its motion. Hence a body rolling down a hill has both K.E and P.E

3. Watt hour

Explanation:

Smallest commercial unit of energy is called Watt hour (Wh). One watt hour is the energy consumed when 1 watt of power is used for 1 hour.

1. U

Explanation:

When you compress a spring, it possess potential energy. The force of compression is proportional to the compression, according to Hooke's Law. Releasing the spring turns the potential energy into kinetic energy. The spring can be then used to propel some object.

3. Both (a) and (b).

2. 2 : 3

2. 1 joule

1. Kilo calorie

Explanation:

The energy stored in food is measured in kilo calories. This is the unit of energy in food. 

Where 1 kilo calorie = 4184 Joules

4. Mechanical

Explanation:

Potential energy is stored in a wound spring. Potential energy is a type of mechanical energy. Hence, energy present in a wound spring is mechanical energy.

3. Half potential and half kinetic energy.

Explanation:

When the body is at height h; its potential energy is at maximum and kinetic energy is zero. When the body hits the ground, its potential energy becomes zero and kinetic energy is at maximum. At mid-way, i.e. half the height; its potential energy becomes half of the maximum potential energy and same happens to the kinetic energy.

4. Initial velocity of the object.

Explanation:

The work done on an object does not depend upon the initial velocity of the moving object.

3. 0J

Explanation:

The girl is moving with the bag on a levelled road. Her direction of motion is perpendicular to the direction of gravitational force. So, work done by the girl against gravity is zero.

1. Does not change.

Explanation:

Potential energy of an object depends only on its position above the ground and mass. So, the potential energy of a car traveling on a leveled road does not change.

2. 800J

Explanation:

Weight of the girl (W) = 400N

Vertical height (h) = 2m

Acceleration due to gravity (g) = 10m/s²

We can calculate the work done against gravity in moving a body of mass (m) by a height (h)  as,

Work done in lifting a body = (Weight of body)(Vertical distance)

So,

W = (m)(g)(h)

So,

Work done in lifting a body

= (400)(2)J

= 800J

1. Acceleration.

Explanation:

Momentum, potential energy and kinetic energy depend on the mass of the body. So, the answer is acceleration as it is independent of mass.

1. Kinetic energy.

Explanation:

A child drops a stone of 1kg from the top of a tower, Kinetic energy of the stone is given by 1250J.

2. The pull of a moving railway engine on its coaches.

Explanation:

1. The weight of a book at rest on a table cannot do any work as the book is at rest. So, the work done by this force is zero.
2. The pulling force applied by the railway engine on its coaches is doing work, as the force applied by the engine results in the motion of the coaches.
3. The tension force in an elastic band wrapped around a parcel cannot do any work, as there is no motion of the parcel because of the tension force of the rubber band.
4. The push of a person’s feet on a floor when he is standing cannot do any work because there is no motion involved due to the applied force.

3. A sparrow in the nest on a tree.

Explanation:

We will justify all statements one by one as:

1. A sparrow flying in the sky possesses kinetic energy, which can be transformed into work.
2. A sparrow moving slowly on the ground possesses kinetic energy, which can be transformed into work.
3. A sparrow in the nest does not possess any kinetic energy as it is at rest. It does not possess the ability to do work in terms of motion of the body.
4. A squirrel going up a tree possesses kinetic energy, which can be transformed into work.

1. As the height increases

Explanation:

Potential energy of an object of mass m at height h, P.E = mgh

              ⟹ P.E ∝ h

Therefore, potential energy increases as the height increases.

3. The weight of the suitcase

Explanation:

The work done by a person in lifting an object is stored as its potential energy mgh.

Hence, work done depends on the weight of the object mg.

3. Ability to do work

Explanation:

Energy is defined as the ability to do work and its SI unit is Joule.

2. Alternator.

Explanation:

Alternator is the device that converts mechanical energy into energy, which runs in microwave oven.

2. Fuel is positive work and that of force of gravity is negative work.

1. Negative, positive or zero

4. A vibrating pendulum when it is just passing through the mean position

Explanation:

Whenever a body is at some height from the mean (base) position or at a state of extension (or contraction), the body will have some potential energy. But when the pendulum is passing the mean position, the height from the base is 0. Hence a vibrating pendulum at the mean position has no potential energy.

2. 10⁶W

Explanation:

Prefix Mega means 10⁶.

So, 1 Megawatt = 1 × 10⁶W

4. A stretched rubber band

Explanation:

Moving vehicle on the road possesses kinetic energy.

A running athlete possesses kinetic energy.

Stone on the road possesses kinetic energy.

A stretched rubber band possesses potential energy.

2. Energy of motion.

2. Joule

2. 40J

2. A scalar quantity

Explanation:

Work done due to displacement caused by a force is a scalar quantity, since it has only magnitude and no direction.

3. Half potential energy and half kinetic energy

Explanation:

When the body is height h; its potential energy is at maximum and kinetic energy is zero. When the body hits the ground, its potential energy becomes zero and kinetic energy is at maximum. At mid-way i.e., half the height; its potential energy becomes half of the maximum potential energy and same happens to the kinetic energy.

4. Mechanical energy

2. Thermal Energy