Physics Mock Test- 1 - Class 9 MCQ

Forces are said to be balanced when two equal and opposite forces acts on an object which makes net force to be zero. Balanced forces are acting means object will be rest. When unbalanced forces are acting on object it starts moving in the direction of force. Example a book kept on table has two forces gravitational force acting downwards and normal force acting upwards. As two forces are equal and opposite the net force will be zero and object remains at rest. and if resultant force is zero the object would be moving with uniform acceleration as there would be no acceleration

So option D is correct

When the bus is not moving the passengers are in the state of rest and they have inertia of rest. When the bus starts moving suddenly, the lower part of the body of passengers, which is in contact with the bus, come in motion, but upper part of their body tends to be in the state of rest and the passengers fall backward.

Work done can be positive,negative and zero. When a body is being lifted in the upward direction, the force of gravity is acting in the downward direction. But, the displacement of the body is in the upward direction. Since the angle between the force and displacement is 180 degrees, the work done by the gravitational force on the body is negative. Diagrammatic representation is given.Hence for negative work done, angle between force and displacement is 180°.

According to the graph given, the body A does not have uniform motion. An object is said to be in uniform motion when it covers equal distances in equal intervals of time. In this case, it accelerates to a particular velocity and remains the same continuously. Otherwise, it is evident that the velocity of B is lesser that A initially and the body B crosses A at X.
Hence, the statement A has uniform motion is not correct.

The correct option is A

A person resting on an armchair.

 

A person in the armchair is at rest, not moving. Hence, the forces are balanced

In water, the particles are much closer together, and they can quickly transmit vibration energy from one particle to the next. This means that the sound wave travels over four times faster than it would in air, but it takesa lot of energy to start the vibration.

Rest and motion are the relative terms because they depend on the observer’s frame of reference.
If an observer is at rest in his or her own frame of reference, but he may be moving in other observer's frame of reference. So if two different observers are not at rest with respect to each other, then they too get different results when they observe the motion or rest of a body.

Elastic Potential Energy:
Elastic potential energy is the energy stored in an elastic object when work is done upon it to compress or stretch it. It is a form of potential energy that is associated with the deformations of elastic materials.
Methods to Achieve Elastic Potential Energy:
The elastic potential energy of a body can be achieved by:
1. Compressing the Body:
- When a force is applied to compress a spring or any elastic object, work is done against the restoring force.
- The energy is stored in the object in the form of potential energy.
- For example, a compressed spring or a stretched rubber band.
2. Stretching the Body:
- When a force is applied to stretch an elastic object, work is done to overcome the elastic force.
- The energy is stored in the object as potential energy.
- For example, a stretched rubber band or a stretched balloon.
Incorrect Options:
A. Setting it into motion: This option does not directly result in the storage of elastic potential energy.
B. Raising the body to a height: This option refers to gravitational potential energy, not elastic potential energy.
C. Using an elastic band to tie the body: Tying a body with an elastic band does not directly result in the storage of elastic potential energy.
Conclusion:
To achieve elastic potential energy, the body needs to be compressed or stretched. This can be done by applying a force to the object, such as compressing a spring or stretching a rubber band. The potential energy is stored in the object due to the deformations caused by the applied force.

Positive Work

- If a force displaces the object in its direction, then the work done is positive

So, W=Fd

The example of this kind of work done is motion of ball falling towards ground where displacement of ball is in the direction of force of gravity.

 

Negative work

- If the force and the displacement are in opposite directions, then the work is said to be negative. For example if a ball is thrown in upwards direction, its displacement would be in upwards direction but the force due to earth’s gravity is in the downward direction.

So here in this case gravity is doing negative work when you throw the ball upwards. Hence the work done by gravitational force is negative. Mathematically when displacement is opposite to the force work done is given by

- Negative work just means that the force and the displacement act in opposite directions.

 

Case of zero work done

- If the directions of force and the displacement are perpendicular to each other, the work done by the force on the object is zero.

For example, when we push hard against a wall, the force we are exerting on the wall does no work, because in this case the displacement of the wall is d = 0. However, in this process, our muscles are using our internal energy and as a result we get tired.

Energy consumed by the household = 250 units
1 unit of energy = 1 kWh = 3.6 x 10⁶ J
∴ 250 units of energy = 250 x 3.6 x 10⁶ 
= 9 x 10⁸ J.

If you rub your hands together for several seconds, you'll notice that your hands feel warm. That warmth is caused by a force called friction. When objects like your hands come in contact and move against each other, they produce friction. Friction happens when you overcome the resistance of one object rubbing against the other. The force of the friction is opposes the direction of the motion. If you just put your hands together, there's no resistance, so there's no friction produced. Rub them together and there's friction.

Since The Body is at Rest ,It clearly means that The Body hasn't covered any Distance here.So,Distance is equal to zero.So,There is no meaning of having any slope here.. So,The Slope=0 Becoz The Distance at anytime will represent same point in Distance-Time Graph at 0..So,(B)is d correct answer. .

Universal gravitational constant is represented by ‘G’. S.I. unit of universal gravitational constant is Nm²/Kg². As G = Fxr²/Mm.

Acceleration = – 4m/s²; Initial speed, u = 60 m s^-1

Time taken = 5s

Acceleration = change in velocity per unit time

a=v-u/t

v= u + at

v = 60 – 4 x 5 = 40 m/s

Correct Answer :- B

Explanation :- When two forces of unequal magnitudes act in opposite directions on an object simultaneously then the object moves in the direction of the force with larger magnitude forces. These forces acting on the object are known as unbalanced forces.

The Gravitational force between two  bodies does not depend on the charge of two bodies.
It is F = Gm1m2 / R²
 

 The technique used by bats to find their way or to locate food is echo-location. 

Sound have the mechanical waves because it required to move their medium (solid, liquid or gas)and sound always move in medium.

Total mechanical energy of the missile = K.E. + P.E.

= 135000 + 637500 = 7.7 × 10⁵J = 772500 J.

Its all because Children below 5-6 years and some small animals like cat, dog, rat etc.. have innovation Sound hearing that's why they can hear sound upto 25Khz.

When the mass of a body increases while keeping the force constant, the acceleration of the body is likely to decrease. This is because acceleration is inversely proportional to mass when force is constant, as described by Newton's second law of motion (F = ma).

- Explanation:
- Increase: Incorrect, as mass and acceleration are inversely proportional when force is constant.
- Remain same: Incorrect, as acceleration changes with mass.
- Decrease: Correct. With increased mass, acceleration decreases.
- Sometimes increases and sometimes decreases: Incorrect; acceleration consistently decreases with increased mass.

Law of Inertia or First law of motion.
As the body tends to be in its original state when the horse suddenly stops, The lower part of the rider stops with it but the upper part remains in motion. So, the rider falls forward.

Pitch is that characteristic of sound that depends on the frequency received by a human ear, and as we know that SI unit of frequency is hertz therefore the unit of quantity on which the pitch of the sound depends is Hertz.

Stethoscope is a medical instrument used by doctors to listen to the sounds produced within the human body, mainly in the heart and lungs, it works on the principle of multiple reflections of sound.