Physics Mock Test- 3 - Class 9 MCQ

Example: When an object moves on horizontal surface, force and displacement acts in same direction. So, work done is positive.

NEGATIVE WORK: The work done is said to be negative work when force and displacement are in opposite direction.

Example: When an object is thrown upwards,the force of gravity is in downward direction whereas displacement acts in upward direction.

ZERO WORK: The work done is said to be zero when force and displacement are perpendicular to each other or when either force or displacement is zero.

Example: When we hold an object and walk, the force acts in downward direction whereas displacement acts in forward direction.

If the degree of force acting on the object is the same ( F = ma) , then as mass increases, acceleration will go down ( a = F / m) . 
So, option ( c) decrease is the correct answer.

GIVEN:-
FORCE PRODUCED IN THE BODY =  F
ACCELERATION PRODUCED WITH FORCE F =  a
ACCELERATION PRODUCED IN OTHER BODY BY SAME FORCE = 4a

To find : Mass of the other body where acceleration produced is 4a

First body -
F = m * a
f/a = m  --------- (eq.01)

Second body - 
Let mass be x
F = X * 4a
F/4a = X   ------(eq.02)

Solving the equation we get-
X = ¼ m

When a hanging carpet is beaten with a stick, the dust particles are removed from it because the carpet on beating suddenly moves forward and the dust particles due to inertia of rest continue to remain at rest. Hence the dust particles fall down and the carpet gets cleaned.

His displacement will be zero although distance covered is non-zero since he ends up where he started.

Displacement can be zero but distance cannot be zero because distance is the total path covered but displacement is the shortest distance between the initial and final position. It can be zero at the end of one round.

Let n be the distance between a and b. Then, the total time taken would be:

n/40 + n/60

And the total distance is 2n. So:

V=distance/time=2n/ n/40 + n/60

=240n/3n+2n

=240/5

=48 m/s

Manish pulls the trolley for a certain distance:- force is applied and there is displacement also , so work is done.

The correct option is A

The object will accelerate in the direction of the applied force.

The object will accelerate in the direction of the applied force.

Absorptive material on the back and side walls will help reduce the reverberation time and unwanted reflections. If possible, try to avoid parallel surfaces, which can cause flutter echoes.

The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear. In the inner ear, the pressure variations are turnedinto electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound.

u = 20 m/s, a = -4 m/s², t = 2 s.
v = ?
∵ v = u + at
⇒ v = 20 + (-4) (2)
⇒ v = 20 - 8 = 12 m/s

Sound is produced when something vibrates. The vibrating body causes the medium (water, air, etc.) around it to vibrate. Vibrations in air are called traveling longitudinal waves, which we can hear.

Force is a phenomenon which is responsible for the change in state or shape or size of a body either from rest to motion or motion to rest.

The correct option is C.
Balanced force:Forces acting on an object which does not change the state of rest or of uniform motion of it are called balanced forces. Unbalanced force:The resultant of two opposite forces acts on an object and brings it in motion. These opposite forces are called unbalanced forces.

Apple falls towards the earth, but the earth does not move towards the apple because acceleration is inversely proportional to mass. Earth’s mass being extremely large as compared to apple, it has negligible acceleration towards the apple.

During reflection, sound waves obey the laws of reflections. To have an appreciable reflection of sound waves from any surface, it should have dimensions equal or larger than the wavelength of the sound waves failing on it. That us, a smaller object will not reflect the sound waves of larger wavelength.

It is used in SONAR (Sound Navigation and Ranging) to determine the depth of the sea and to locate underwater objects like sunken ships, hills, icebergs, etc. The formula used is:

2d = v × t

Where, d = depth of the sea

v = velocity of the sound in the medium

t = time interval between transmission and reception of the ultrasounds.

It is used to detect cracks and flaws in metal blocks.

(b) We are given,

Initial velocity of both the bus and the van = v

Final velocity of both the bus and the van = 0

If m₁ and m₂ are the masses of the large bus and the van respectively, where m₁ is much greater than m₂

Change in momentum of the bus = m₁ x (0 — v) = —m₁v

Change in momentum of the van = m₂ x (0 — v) = —m₂v

Since m₁ < m₂, the van will experience smaller momentum change.

(c) The force acting on a body is equal to the product of its mass and the acceleration, i.e.,

F= mass x acceleration = m x a

a = F ÷ m

a α 1 ÷ m

Acceleration experienced by the bus α 1 ÷ m₁

Acceleration experienced by the van , α 1 ÷ m₂

Since m₂ < m₁, therefore the van experiences greater acceleration.

(d) Due to the transfer of small momentum from the van to the bus, the bus suffers less damage than the van.

The correct option is B.
 Objects of different masses falling freely near the surface of the earth would have the same velocities at any instant because they will have the same acceleration due to gravity.

Correct Answer :- c

Explanation : An empty closed drum and a filled drum of same dimension will bring same upthrust and same volume

• Gravitational force is acting in the downward direction. As we know every action has a reaction.
• So, there is an equal and opposite force acting in opposite direction also.