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Laws of Motion Test - 7

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Laws of Motion Test - 7

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Question 1
1 / -0

When several forces act on a body

A
the effect on its motion is the same as when a single force, equal to the vector sum (resultant) of the forces, acts on the body

B
the effect on its motion is the same as when a single force, algebric sum only in horizontal direction, acts on the body

C
the effect on its motion is the same as when a single force acts on the body

D
The effect on its motion will be equal to a single force equal to the algebric sum of the forces

Solution

Force is a vector quantity. When several forces act on a body the effect on its motion is the same as when a single force, equal to the vector sum (resultant) of the forces, acts on the body
Question 2
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Inertia refers to

A
resistance to change

B
slow motion

C
ease of motion

D
dullness

Solution

Inertia is the resistance of any physical object to any change in its state of motion; this includes changes to its speed, direction, or state of rest. It is the tendency of objects to keep moving in a straight line at constant velocity. Inertia is a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.
Question 3
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What should be the tension in a rope pulling vertically upward a mass of 100 kg so that starting from rest, it acquires a velocity of 4 m/s in 1.5 sec?

A
^{_{1267 N}}

B
^{1125 N}

C
^{1140 N}

D
^{1054 N}
Question 4
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According to Newton's second law of motion

A
The momentum of a body is directly proportional to the applied force and takes place in the direction in which the force acts

B
The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction in which the force acts

C
The intergration of momentum of a body is directly proportional to the applied force and takes place in the direction in which the force acts

D
The momentum of a body is directly proportional to the applied force and takes place in the direction opposite to the force

Solution

If mass does not change then acceleration of a particle is dependent on the forces acting upon the particle and the particle's mass. For a given particle, if the net force is increased, the acceleration is increased. For a given net force, the more mass a particle has, the less acceleration it has.

hence the rate of change of momentum of a body is directly proportional to the applied force
Question 5
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Directions: The following question has four choices out of which ONLY ONE is correct.

A cyclist turns around a curve at 15 km/hr. If he turns at double the speed, the tendency to overturn is

A
doubled

B
quardrupled

C
halved

D
unchanged
Question 6
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Force is a

A
qualitative measure of the interaction between two bodies

B
qualitative measure of the momentum of two bodies

C
quantitative measure of the interaction between two bodies

D
quantitative measure of the momentum between two bodies

Solution

Newton's second law of motion gives the quantitative definition of force. The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object
Question 7
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A given object takes n times as much time to slide down a 45° rough incline as it takes to slide down a perfectly smooth 45° incline. The coefficient of kinetic friction between the object and the incline is given by

A

B

C

D
Question 8
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A stationary body of mass 3 kg explodes into three identical pieces. Two of the pieces fly off at right angles to each other, one with a velocity m/s and the other with a velocitym/s. If the explosion takes place in 10^-5s, the average force (in Newton) acting on the third piece is

A

B

C

D
Question 9
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Force F at a point in space (location of the particle) at a certain instant of time t is

A
related to acceleration a at that point at next instant.

B
related to acceleration a at that point at previous instant.

C
related to acceleration a at previous point at that instant.

D
related to acceleration a at that point and the same instant.

Solution

According to Newton's second law of motion the acceleration of a point mass as produced by a net force is directly proportional to the magnitude of the net force at that point in the same direction as the net force at that instant
F = ma
Question 10
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Directions: The following question has four choices out of which ONLY ONE is correct.

The maximum and minimum tension in the string whirling in a circle of radius 2.5 m with constant velocity are in the ratio 5 : 3 then its velocity is (g = 9.8 m/s²)

A

B
7 m/s

C

D
m/s
Question 11
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Directions: The following question has four choices out of which ONLY ONE is correct.

_{What is the value of linear velocity, if angular velocity is 3}_{– 4}₊_{and distance from the centre is 5}_{– 6}_{+ 6}_?

A
₆_{– 6}_{+ 3}

B
_{– 18}_{– 13}_{+ 2}

C
₄_{– 13}_{+ 6}

D
₆_{– 2}_{+ 8}
Question 12
1 / -0

The force acting on a freely falling body in terms of mass m and acceleration due to gravity g is

A
F = m g

B
F = m² g

C
F = m g²

D
F = m⁻² g

Solution

according to newton's second law of motion
F = ma
here acceleration is due to gravity and is equal to g.
So that for a freely falling body
F = mg
Question 13
1 / -0

Two blocks of equal mass m are released from the top of a smooth fixed wedge as shown in the figure. The acceleration of the center of mass of the two blocks is

A
g

B

C

D
Question 14
1 / -0

The force on a rocket, moving with a velocity of 300 m/s is 210 N. Then, the rate of combustion of the fuel will be

A
3.5 kg/sec

B
2.1 kg/sec

C
1.4 kg/sec

D
0.7 kg/sec
Question 15
1 / -0

Two blocks of masses m₁ = 3 m and m₂ = 2 m are suspended from a rigid support by two inextensible uniform wires A and B. Wire A has negligible mass and wire B has a mass m₃ = m as shown in the figure. The whole system of blocks, wires and the support has an upward acceleration a.

The tension at the midpoint C of wire B is

A

B

C

D
Question 16
1 / -0

A cubical block of mass 'm' rests on a rough horizontal surface. μ is the coefficient of static friction between the block and the surface. A force mg, acting on the cube at an angle θ with the vertical side of the cube, pulls the block. If the block is to be pulled along the surface, then the value cot(θ/2) is

A
less than μ

B
greater than μ

C
equal to μ

D
not dependent on μ
Question 17
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A ball of mass 0.6 kg attached to a light inextensible string rotates in a vertical circle of radius 0.75 m. It has a speed of 5 ms^-1 when the string is horizontal. Tension in string when it is horizontal on the other side is (Take g = 10 ms^-2)

A
30 N

B
26 N

C
20 N

D
6 N
Question 18
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Impulse is

A
the average of force over a short period

B
the integral of force over a short period

C
the derivative of force over a short period

D
the difference of force over a short period

Solution

A resultant force causes acceleration and a change in the velocity of the body for as long as it acts.The change in momentum is equal to the product of the average force and duration. Conversely, a small force applied for a long time produces the same change in momentum, the same impulse, as a larger force applied for a short time interval.

Impulse J is

The impulse is the integral of the resultant force (F) with respect to time
Question 19
1 / -0

The second law of motion is a vector law. It is equivalent to

A
One equation, one for each component of the vectors

B
Two equations, one for each component of the vectors

C
Three equations, one for each component of the vectors

D
Four equations, one for each component of the vectors and one for time

Solution

F_x= ma_x, F_y= ma_y, F_z= ma_z
Question 20
1 / -0

Momentum of a body is

A
a scalar equal in magnitude to the product of mass and velocity

B
a vector equal in magnitude to the product of mass and instantaneous velocity and direction being that of instantaneous velocity

C
a vector equal in magnitude to the product of mass and acceleration and direction being that of velocity

D
a vector equal in magnitude to the product of mass and average speed and direction being that of velocity

Solution
Question 21
1 / -0

A small block is shot into each of the four tracks as shown below. Each of the frictionless tracks rises to the same height. The speed with which the block enters the tracks is the same in all the cases. At the highest point of the track, normal reaction is the maximum in

A

B

C

D
Question 22
1 / -0

The minimum force required to move a body up an inclined plane of inclination 30^o is found to be thrice the minimum force required to prevent it from sliding down the plane. The coefficient of friction between the body and the plane is

A

B

C

D
Question 23
1 / -0

A block of mass 5 kg is resting on an inclined plane. The inclination of the plane to the horizontal direction is gradually increased. It is found that when the angle of inclination is 30°, the block just begins to slide down the plane. The coefficient of sliding friction between the block and the plane is

A
= sin 30^o

B
= cos 30^o

C
= tan 30^o

D
= cot 30^o
Question 24
1 / -0

The figure shows two blocks A and B pushed against a smooth wall with force F. The wall is smooth, but the surface of contact of A and B is rough. Which of the following is true for the system of blocks?

A
The system cannot be in equilibrium.

B
F should be equal to the total weight of A and B.

C
F should be less than the total weight of A and B.

D
F should be more than the total weight of A and B.
Question 25
1 / -0

If second law is applied to a rigid body

A
the acceleration is that of any particle in the body

B
the acceleration is the average of all particles in the body

C
the acceleration is that of the centre of mass

D
none of the above

Solution

a rigid body is characterized by the fact that the distances between any two particles that make up the body is constant in time. This means that instead of talking about the motion of each particle, we can talk about the motion of any one point in the body and of the body as a whole with reference to this one particle. The most convenient choice for this one point is the Centre of Mass

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