Equilibrium of Forces — MH-CET Physics MCQs with Solutions
Free MH-CET Physics Equilibrium of Forces MCQs with step-by-step solutions (20 questions). Part of Laws of Motion (Std 11). Practise online on Prepizo — no login needed.
▶ Practise Equilibrium of Forces online (free)
Questions with solutions
Q1 — Equilibrium of Forces · easy · theory
A body is in translational equilibrium when:
A. It is stationary only
B. The vector sum of all forces acting on it is zero ✓ Correct
C. The sum of the magnitudes of the forces is zero
D. The net torque on it is zero
Solution: Zero net torque gives rotational equilibrium, which is a separate condition.
Q2 — Equilibrium of Forces · medium · theory
Concurrent forces are forces whose:
A. Magnitudes are equal
B. Lines of action meet at a single point ✓ Correct
C. Directions are parallel
D. Resultant is always zero
Solution: Such forces can be combined by the ordinary laws of vector addition.
Q3 — Equilibrium of Forces · medium · theory
If three concurrent forces keep a body in equilibrium, they can be represented by:
A. Three parallel lines
B. The three angles of a triangle
C. The three medians of a triangle
D. The three sides of a triangle taken in order ✓ Correct
Solution: The triangle closes precisely because the resultant is zero.
Q4 — Equilibrium of Forces · medium · theory
Lami's theorem applies to:
A. Any number of forces
B. Two forces only
C. Non-concurrent forces
D. Three concurrent coplanar forces in equilibrium ✓ Correct
Solution: It states that each force is proportional to the sine of the angle between the other two.
Q5 — Equilibrium of Forces · medium · theory
A body in rotational equilibrium has:
A. Zero net torque about any axis ✓ Correct
B. Zero angular velocity necessarily
C. Zero moment of inertia
D. Zero net force only
Solution: A body may rotate at constant angular velocity and still be in rotational equilibrium.
Q6 — Equilibrium of Forces · medium · theory
A body is in stable equilibrium if, on being slightly displaced, it:
A. Moves further away from its original position
B. Begins to rotate uniformly
C. Tends to return to its original position ✓ Correct
D. Remains in the new position
Solution: Its potential energy is a minimum in the equilibrium position.
Q7 — Equilibrium of Forces · medium · theory
A couple acting on a body produces:
A. Rotation without translation, since the net force is zero ✓ Correct
B. Neither translation nor rotation
C. Both translation and rotation
D. Translation without rotation
Solution: The two equal and opposite forces have different lines of action.
Q8 — Equilibrium of Forces · easy · theory
A body moving with constant velocity is:
A. Not in equilibrium, since it is moving
B. In equilibrium, since the net force on it is zero ✓ Correct
C. Never in equilibrium
D. In equilibrium only if it is also rotating
Solution: Equilibrium requires zero acceleration, not zero velocity.
Q9 — Equilibrium of Forces · medium · numerical
Two perpendicular forces of $3\text{ N}$ and $4\text{ N}$ act on a body. The third force needed to keep it in equilibrium is:
A. $12\text{ N}$
B. $1\text{ N}$
C. $7\text{ N}$
D. $5\text{ N}$ ✓ Correct
Solution: Their resultant is $\sqrt{9 + 16} = 5\text{ N}$, so the balancing force is $5\text{ N}$ in the opposite direction.
Q10 — Equilibrium of Forces · medium · numerical
Two perpendicular forces of $5\text{ N}$ and $12\text{ N}$ act on a body. The balancing force is:
A. $17\text{ N}$
B. $13\text{ N}$ ✓ Correct
C. $7\text{ N}$
D. $60\text{ N}$
Solution: The resultant is $\sqrt{25 + 144} = 13\text{ N}$.
Q11 — Equilibrium of Forces · hard · numerical
Three equal forces acting on a body keep it in equilibrium. The angle between any two of them is:
A. $90^\circ$
B. $60^\circ$
C. $120^\circ$ ✓ Correct
D. $180^\circ$
Solution: Three equal vectors sum to zero only when they are symmetrically placed at $120^\circ$.
Q12 — Equilibrium of Forces · hard · numerical
Two forces of $10\text{ N}$ each act at $60^\circ$ to each other. The force needed to balance them is approximately:
A. $10\text{ N}$
B. $20\text{ N}$
C. $14.1\text{ N}$
D. $17.3\text{ N}$ ✓ Correct
Solution: Their resultant is $\sqrt{100 + 100 + 100} = \sqrt{300} \approx 17.3\text{ N}$.
Q13 — Equilibrium of Forces · easy · numerical
A body of mass $5\text{ kg}$ hangs at rest from a string. The tension in the string is ($g = 10\text{ m/s}^2$):
A. $500\text{ N}$
B. $5\text{ N}$
C. $50\text{ N}$ ✓ Correct
D. $0.5\text{ N}$
Solution: For equilibrium the tension balances the weight: $T = mg = 50\text{ N}$.
Q14 — Equilibrium of Forces · hard · numerical
A block of mass $4\text{ kg}$ rests on a smooth incline of $30^\circ$, held by a force along the incline. That force is ($g = 10\text{ m/s}^2$):
A. $20\text{ N}$ ✓ Correct
B. $10\text{ N}$
C. $34.6\text{ N}$
D. $40\text{ N}$
Solution: It must balance the component of weight along the incline: $mg\sin 30^\circ = 40 \times 0.5 = 20\text{ N}$.
Q15 — Equilibrium of Forces · hard · numerical
Three concurrent forces of $6\text{ N}$, $8\text{ N}$ and $10\text{ N}$ can keep a body in equilibrium because:
A. They can form a closed triangle, since $6^2 + 8^2 = 10^2$ ✓ Correct
B. They are all different
C. Their magnitudes add to an even number
D. The largest exceeds the sum of the others
Solution: A closed force triangle is exactly the condition for three forces to be in equilibrium.
Q16 — Equilibrium of Forces · hard · numerical
A weight of $100\text{ N}$ is supported symmetrically by two strings making $90^\circ$ with each other. The tension in each string is approximately:
A. $70.7\text{ N}$ ✓ Correct
B. $141.4\text{ N}$
C. $100\text{ N}$
D. $50\text{ N}$
Solution: Each vertical component is $50\text{ N}$, and with each string at $45^\circ$ to the vertical, $T = \dfrac{50}{\cos 45^\circ} \approx 70.7\text{ N}$.
Q17 — Equilibrium of Forces · medium · numerical
For a body in equilibrium under three forces, the resultant of any two must be:
A. Zero
B. Equal to the third in both magnitude and direction
C. Perpendicular to the third
D. Equal in magnitude and opposite in direction to the third ✓ Correct
Solution: Only then does the vector sum of all three vanish.
Q18 — Equilibrium of Forces · easy · numerical
A body under the action of several forces has zero acceleration. The net force on it is:
A. Equal to its weight
B. Zero ✓ Correct
C. Equal to the largest force
D. Perpendicular to its velocity
Solution: $F = ma$ with $a = 0$ requires the net force to vanish.
Q19 — Equilibrium of Forces · medium · numerical
Two forces of $8\text{ N}$ and $6\text{ N}$ act at right angles. The single force that would balance them is:
A. $10\text{ N}$ ✓ Correct
B. $14\text{ N}$
C. $48\text{ N}$
D. $2\text{ N}$
Solution: Their resultant is $\sqrt{64 + 36} = 10\text{ N}$.
Q20 — Equilibrium of Forces · hard · numerical
A block rests on a rough horizontal surface with no applied force. The frictional force on it is:
A. Equal to $mg$
B. Equal to $\mu mg$
C. Equal to the normal reaction
D. Zero ✓ Correct
Solution: Static friction is self-adjusting and only arises to oppose an applied force or a tendency to move.