NEET Physics Centre of Mass Centre of Gravity and Principle of Moments MCQs Set A

Question. The position of centre of mass of a system of particles does not depend upon the
(a) relative distance between the particles
(b) position of the particles
(c) symmetry of the body
(d) mass of particles

Answer: A

Question. The motion of the centre of mass depends on
(a) total external forces
(b) total internal forces
(c) Both
(d) None of these

Answer: A

Question. The centre of mass of two particles lies on the line
(a) joining the particles
(b) perpendicular to the line joining the particles
(c) at any angle to this line
(d) None of these

Answer: A

Question. A pulley fixed to the ceiling carries a string with blocks of mass m and 3 m attached to its ends. The masses of string and pulley are negligible. When the system is released, its centre of mass moves with what acceleration ?
(a) g/2
(b) – g/2
(c) – g/4
(d) 0

Answer: A

Question. In rotatory motion, linear velocities of all the particles of the body are
(a) different
(b) zero
(c) cannot say
(d) same

Answer: A

Question.  The motion of a rigid body which is not pivoted or fixed in some way is either a pure ...A... or a combination of translation and rotation. The motion of a rigid body which is pivoted or fixed in some way is ...B... Here, A and B refer to
(a) translation and rotation
(b) rotation and translation
(c) translation and the combination of rotation and translation
(d) None of the above

Answer: A

Question. If the resultant of all external forces is zero, then velocity of centre of mass will be
(a) either (a) or (b)
(b) zero
(c) constant
(d) neither (a) nor (b)

Answer: A

Question. In rotation of a rigid body about a fixed axis, every ...A...of the body moves in a ...B..., which lies in a plane ...C... to the axis and has its centre on the axis. Here, A, B and C refer to
(a) particle, circle and perpendicular
(b) particle perpendicular and perpendicular
(c) circle, particle and perpendicular
(d) particle, perpendicular and circle

Answer: A

Question. Centre of mass of the earth and the moon system lies
(a) closer to the earth
(b) closer to the moon
(c) at the mid-point of line joining the earth and the moon
(d) cannot be predicted

Answer: A

Question. Consider the following statements and choose the correct option.
I. Position vector of centre of mass of two particles of equal mass is equal to the position vector of either particle.
II. Centre of mass is always at the mid-point of the line joining two particles
III. Centre of mass of a body can lie where there is no mass
(a) III only
(b) I, II and III
(c) II only
(d) I and II

Answer: A

Question. There are some passengers inside a stationary railway compartment. The centre of mass of the compartment itself (without the passengers) is C₁, while the centre of mass of the ‘compartment plus passengers’ system is C₂. If the passengers move about inside the compartment then
(a) C₁ will move but C₂ will be stationary with respect to the ground
(b) C₂ will move but C₁ will be stationary with respect to the ground
(c) neither C₁ nor C₂ will be stationary with respect to the ground
(d) both C₁ and C₂ will move with respect to the ground

Answer: A

Question. A stick is thrown in the air and lands on the ground at some distance from the thrower. The centre of mass of the stick will move along a parabolic path
(a) in all cases
(b) only if the stick is uniform
(c) only if the stick has linear motion but no rotational motion
(d) only if the stick has a shape such that its centre of mass is located at some point on it and not outside it

Answer: A

Question. Assertion : The centre of mass of a two particle system lies on the line joining the two particle, being closer to the heavier particle.
Reason : Product of mass of particle and its distance from centre of mass is numerically equal to product of mass of other particle and its distance from centre of mass.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.

Answer: A

Question. Three masses are placed on the x-axis : 300 g at origin, 500 g at x = 40 cm and 400 g at x = 70 cm. The distance of the centre of mass from the origin is
(a) 40 cm
(b) 45 cm
(c) 50 cm
(d) 30 cm

Answer: A

Question. Assertion : The centre of mass of an isolated system has a constant velocity.
Reason : If centre of mass of an isolated system is already at rest, it remains at rest.
(a) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(b) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct

Answer: A

Question. A shell following a parabolic path explodes somewhere in its flight. The centre of mass of fragments will continue to move in
(a) same parabolic path
(b) any direction
(c) vertical direction
(d) horizontal direction

Answer: A

Question. A man stands at one end of a boat which is stationary in water. Neglect water resistance. The man now moves to the other end of the boat and again becomes stationary. The centre of mass of the ‘man plus boat’ system will remain stationary with respect to water
(a) in all cases
(b) only when the man is stationary initially and finally
(c) only if the man moves without acceleration on the boat
(d) only if the man and the boat have equal masses

Answer: A

Question. Statement 1 : When you lean behind over the hind legs of the chair, the chair falls back after a certain angle.
Statement 2 : Centre of mass lying outside the system makes the system unstable.
(a) Statement -1 is true, Statement-2 is false
(b) Statement -1 is true, Statement-2 is true; Statement -2 is not a correct explanation for Statement-1
(c) Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
(d) Statement -1 is false, Statement-2 is true

Answer: A

Question. A system consists of three particles, each of mass m and located at (1, 1), (2, 2) and (3, 3). The co-ordinates of the centre of mass are
(a) (2, 2)
(b) (3, 3)
(c) (6, 6)
(d) (1, 1)

Answer: A

Question. Two bodies of masses 2 kg and 4 kg are moving with velocities 2 m/s and 10 m/s respectively along same direction. Then the velocity of their centre of mass will be
(a) 7.3 m/s
(b) 6.4 m/s
(c) 5.3 m/s
(d) 8.1 m/s

Answer: A

Question.  Two objects P and Q initially at rest move towards each other under mutual force of attraction. At the instant when the velocity of P is v and that of Q is 2v, the velocity of centre of mass of the system is
(a) zero
(b) 2v
(c) 3v
(d) v

Answer: A

Question. The position of centre of mass of a system of particles does not depend upon the
(a) None of these
(b) position of the particles
(c) symmetry of the body
(d) mass of particles

Answer: A