Test: Forces & Laws of Motion- 5


25 Questions MCQ Test Science & Technology for UPSC CSE | Test: Forces & Laws of Motion- 5


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QUESTION: 1

An external influence which changes or tends to change the state of rest or uniform motion of body or its
dimensions is called :

Solution:

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.

QUESTION: 2

Equal and opposite forces acting on a body which do not change its state of rest or uniform motion are called:

Solution:

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.

QUESTION: 3

The unequal and opposite forces acting on a body, which change its state of rest or uniform motion are called:

Solution:

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.

QUESTION: 4

Force of friction always acts in the direction:

Solution:
QUESTION: 5

When balanced forces act on a body, the body:

Solution:

According to the law of inertia or Newton's first law of motion, a body in state of rest or of uniform motion remains in state of rest or of uniform motion unless it is acted upon by an external force. Hence a body in uniform motion required no force to keep them in uniform motion.

QUESTION: 6

When unbalanced forces act on a body, the body:

Solution: The Second Law of Motion states that if an unbalanced force acts on a body, that body will experience acceleration ( or deceleration), that is, a change of speed.
 One can say that a body at rest is considered to have zero speed, ( a constant speed). So any force that causes a body to move is an unbalanced force. Also, any force, such as friction, or gravity, that causes a body to slow down or speed up, is an unbalanced force. 

QUESTION: 7

If no external force acts on a body, it will :

Solution:
QUESTION: 8

If a body is allowed ti freely fall from a height, its speed increases continuously. It is because:

Solution:

The gravitational force for a falling object is along the direction of motion. Hence, its speed increases continuously till  it touches the ground.

QUESTION: 9

A force of magnitude' F' acts on a body of mass 'm'. The acceleration of the body depends upon:

Solution:

F = m × a 
Where, F = force
m = mass
a = acceleration

QUESTION: 10

Force remaining constant, if the mass of body increases, its acceleration is likely to :

Solution:
QUESTION: 11

A force F produces an acceleration 'a' in a body. The same force produces and acceleration 4a in another
body. The mass of other body is :

Solution:
QUESTION: 12

When a running motorbike accelerates suddenly, the pillion rider has a tendency to fall backward. This is an example of:

Solution:

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.

QUESTION: 13

A force F acts on a stationary body for the time t. The distance covered by the body 'S' will be proportional to:

Solution: S=ut+1/2at^2 Since the mass is constant, and i guess you dont mean above to be dealt in relativistic speed, and a constant force is applied then we will have constant acceleration. So distance covered will be only dependent on elapsed time t.So s ∝ t^2
QUESTION: 14

The impact which a body can produce due to the combined effect of mass and velocity is called:

Solution:

Mass ad velocity both are considered to be quantities which defines motion.

The combination of both is called quantity of motion. It is momentum.

P = mv

QUESTION: 15

The SI unit of momentum is :

Solution:

If we consider the situation when force is equivalent to the rate of change of momentum. I.e Force = (change in momentum)(time interval)
 then, change in momentum = Force * (time interval).
Therefore, the unit for momentum can be Newton - second (Ns)

QUESTION: 16

The tendency of a body to continue in its state of rest or uniform motion, even on the application of external force is called:

Solution:

The intrinsic property of material body which resists a change in its state of rest or of uniform
motion along a straight line is called inertia.
Inertia is a natural tendency of the body. Mass is taken as a quantitative measure of inertia of a
material body. The larger the mass of a body the greater the difficulty in bringing about a change in its
state of motion, i.e. the mass is a measure of inertia.

QUESTION: 17

A body will continue in its state of rest or uniform motion in a straight line, unless acted by some external force. The statement represents :

Solution: Body is in the motion it tends to be in motion and when a body is in the rest it tends to be in rest unless and external force is not applied on it.
QUESTION: 18

The magnitude of inertia of a body is determined by its:

Solution:
QUESTION: 19

Momentum is a:

Solution:

Momentum is a vector quantity. For a particle with mass, the momentum equals mass times velocity, and velocity is a vector quantity while mass is a scalar quantity. A scalar multiplied by a vector is a vector. A moving body would be a particle with a mass.

QUESTION: 20

A body P has mass 2 m and velocity 5 v. Another body Q has mass 8 m and velocity 1.25 v. The ratio of momentum of P and Q is :

Solution:
Momentum = mass x velocity  
Therefore in first case momentum = 2m x 5v = 10mv
​Therefore in second case momentum = 8m x 1.25v = 10mv
​Thus in both the cases momentum is the same, so, Ratio is 1:1
QUESTION: 21

The magnitude of a physical quantity is 8.5 Ns. The physical quantity is :

Solution: The newton second (also newton-second, symbol N s or N·s) is the derived SI unit of impulse. It is dimensionally equivalent to the momentum unit kilogram metre per second (kg·m/s). One newton second corresponds to a one-newton force applied for one second. Derivation- p=mv =kg×m/s =kgm/s×s/s =kgm/s^2×s =N×s
QUESTION: 22

There is a rubber ball and a stone ball of same size. If both balls are at rest:

Solution:
QUESTION: 23

When we vigorously a shake branch of a tree, some leaves get detached. It is due to the:

Solution:
QUESTION: 24

When the driver of a fast moving car suddenly applies brakes, the passengers in the car:

Solution:
QUESTION: 25

Which is the incorrect statement? A spaceship continues moving in space with uniform speed because:

Solution: A spaceship continues moving in space with uniform speed because no force of gravitation acts on it but not it's mass is zero in space and everything in the space appear to be floating that is why the astronauts also appear to float in space but their mass is not zero actually.

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