Equilibrium of Forces MCQs for NEET

Force can be defined as any action that tends to change the state of rest or motion of a body to which it is applied. Following three characteristic parameters describe a force:

  • Magnitude
  • Point of Application
  • Direction of Application

The equilibrium law states that two forces can be in equilibrium only if they are equal in magnitude, opposite in direction and collinear in action. The action of any given system of forces on a rigid body will not be changed if we add to or subtract from another system of forces in equilibrium

Question and Answer

1. How is the weight of the aeroplane flying in the air balanced?

  1. The weight is balanced because of the force due to the pressure difference between the upper and lower surfaces of the wings created by different airspeeds on the surfaces.
  2. The weight is balanced due to the vertical component of the thrust created by air currents striking the lower surface of the wings
  3. The weight is balanced due to the force produced when the reactions of gases are ejected by the revolving propellor.
  4. Upthrust of the air which will be equal to the weight of the air having the same volume as the plane

Answer: (a) The weight is balanced because of the force due to the pressure difference between the upper and lower surfaces of the wings created by different airspeeds on the surfaces.

2. Which of the following is true when a body is stationary?

  1. The force acting on it is not in contact with it
  2. The body is in vacuum
  3. There is no force acting on it
  4. The combination of forces acting on it balance each other

Answer: (d) The combination of forces acting on it balance each other

3. Two forces with magnitude F have the resultant of same magnitude F. What is the angle between the forces?

  1. 450
  2. 600
  3. 1200
  4. 1500

Answer: (c) 1200

4. What is the angle between the forces if two forces with equal magnitudes F act on a body and the magnitude of the resultant force is F/3?

  1. \(\begin{array}{l}\cos^{-1}\left ( \frac{17}{18} \right )\end{array} \)
  2. \(\begin{array}{l}\cos^{-1}\left ( \frac{2}{3} \right )\end{array} \)
  3. \(\begin{array}{l}\cos^{-1}\left ( \frac{8}{19} \right )\end{array} \)
  4. \(\begin{array}{l}\cos^{-1}\left (- \frac{1}{3} \right )\end{array} \)

Answer: (a)

\(\begin{array}{l}\cos^{-1}\left ( \frac{17}{18} \right )\end{array} \)

5. In which direction should the force be applied to balance a force in the direction of North-East direction?

  1. South
  2. West
  3. South-West
  4. North-East

Answer: (c) South-West

6. Among the following which cannot be a resultant force of 5 N and 10 N?

  1. 4 N
  2. 5 N
  3. 8 N
  4. 12 N

Answer: (a) 4 N

7. The resultant of the two forces are perpendicular to the smaller of the two forces. The magnitude of one of the forces is double the magnitude of the other force. What is the angle between the forces?

  1. 600
  2. 900
  3. 1200
  4. 1500

Answer: (c) 1200

\(\begin{array}{l}8. \ Which \ of \ the \ following \ depictions \ correctly \ shows \ the \ vector \ addition \ of \ forces \ \   \vec{F_1} \ and \ \vec{F_2} \ to \ yield \ a \ third \ force \ \vec{F_3}?\end{array} \)

 

9. Which of the following sets of concurrent forces are in equilibrium?

  1. \(\begin{array}{l}{F_1}=3\,N,{F_2}=5\,N, {F_3}=1\,N\end{array} \)
  2. \(\begin{array}{l}{F_1}=3\,N,{F_2}=5\,N, {F_3}=6\,N\end{array} \)
  3. \(\begin{array}{l}{F_1}=3\,N,{F_2}=5\,N, {F_3}=9\,N\end{array} \)
  4. \(\begin{array}{l}{F_1}=3\,N,{F_2}=5\,N, {F_3}=15\,N\end{array} \)

Answer: (b)

\(\begin{array}{l}{F_1}=3\,N,{F_2}=5\,N, {F_3}=6\,N\end{array} \)

10. Two blocks connected to each other by a string is hung to the ceiling by connecting another string to the upper block. When a force F is applied on the string, it produces an acceleration of 2 m/s2. If T and T’ are the tensions in two parts of the string, then which of the following is true?

  1. T = 70.8 N and T’= 47.2 N
  2. T = 70.8 N and T’= 0
  3. T = 70.8 N and T’= 58.8 N
  4. T = 58.8 N and T’= 47.2 N

Answer: (a) T = 70.8 N and T’= 47.2 N

11. Consider the blocks shown in the diagram to be pushed against a frictionless table by a constant force. Following statements are said about the blocks:

  • All blocks move with the same acceleration
  • The net force on all the blocks is the same

Which of these statements is true?

  1. Both A and B
  2. Neither A and B
  3. Only A
  4. Only B

Answer: (c) Only A

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