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.

The speedometer of a car measures:

• The speedometer indicates instantaneous speed, which is the speed of the car at any specific moment.

• Unlike average speed, which is calculated over a distance and time, the speedometer provides real-time data.

• This measurement helps drivers maintain safe speeds and comply with road regulations.

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
 

A weightless balloon containing 200 g of water will not displace its weight in water. This is because the balloon is effectively weightless and does not exert any downward force in the water. Here are some key points to understand this concept:

• The buoyant force acting on an object submerged in water equals the weight of the water displaced.
• In this case, the balloon is weightless, meaning it does not contribute to the overall weight in water.
• Therefore, when placed in water, the balloon will not weigh anything, as it is not affected by buoyancy like a regular object would be.

The conclusion is that the weight of a weightless balloon in water is zero.

School bags have a broader base to reduce

• Pressure: A wider base helps distribute the weight evenly, which reduces the pressure on the back.
• Weight: The design can make the bag feel lighter, as the weight is better balanced.
• Air resistance: A broader base can help minimise drag, allowing for easier movement.
• Normal reaction: This term refers to the support force exerted by a surface. A wider base provides a more stable support.

Therefore, Correct answer is A.

 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.

Given a force F that produces an acceleration 'a' in one body, and the same force producing an acceleration of 4a in another body, we can analyse the relationship between mass and acceleration.

According to Newton's second law of motion, the relationship between force, mass, and acceleration is expressed as:

• F = m × a, where F is the force, m is the mass, and a is the acceleration.

For the first body, we have:

• F = m1 × a

For the second body, where the acceleration is 4a:

• F = m2 × 4a

Since both bodies are acted upon by the same force, we can equate their expressions:

• m1 × a = m2 × 4a

By simplifying this equation, we can eliminate 'a' (provided a is not zero):

• m1 = 4m2

This shows that the mass of the first body is four times the mass of the second body:

• m2 = m1/4

Therefore, the mass of the second body is four times less than the mass of the first body.

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.

The solid has a relative density of 0.6, which indicates that it is less dense than water. This property allows it to float. Here’s how this affects its submerged volume:

• Relative density is defined as the ratio of the density of a substance to the density of a reference substance, typically water.
• Since the solid's relative density is 0.6, it means that 60% of its volume will be submerged when floating in water.
• The remaining 40% of the solid's volume will be above the water's surface.

Therefore, the solid will float with 60% of its volume inside the water.

The least value of apparent weight of a body in a fluid is an important concept in physics. The apparent weight refers to the weight of an object when it is submerged in a fluid, accounting for the buoyant force acting on it.

Key points to understand this concept include:

• The apparent weight can be calculated by subtracting the buoyant force from the actual weight of the object.
• If the buoyant force equals the weight of the object, the apparent weight becomes zero, meaning the object floats.
• When the object is fully submerged, it may still have a positive apparent weight if it is denser than the fluid.
• In the case of lighter objects, they may experience an apparent weight of zero or even a negative value when the buoyant force exceeds their weight.

Therefore, the least value of apparent weight of a body in a fluid is zero, which occurs when the object is neutrally buoyant.