Which of the following statements give characteristics of contact forces? 1. It appears between an object when it is in contact with some other object 2. It satisfies the third law of motion 3. It may appear between a pair of solid and fluid Select the answer using the code given below:
- (a)1 and 3 only
- (b)2 and 3 only
- (c)1 and 2 only
- (d)1, 2 and 3
Correct — D, all three (1, 2 and 3). A contact force is one that acts only when two bodies physically touch, so statement 1 is its defining property. Statement 2 is true because EVERY force — contact forces included — comes in an equal-and-opposite action-reaction pair, i.e. obeys Newton's third law. Statement 3 is true because a solid immersed in or moving through a fluid experiences contact forces such as viscous drag, fluid friction and buoyancy. All three are genuine characteristics, so the answer is 1, 2 and 3.
- (a)1 and 3 only — This drops statement 2, but 2 is true — contact forces do satisfy Newton's third law, since all forces occur as action-reaction pairs.
- (b)2 and 3 only — This drops statement 1, yet 1 is the very definition of a contact force (it appears only when bodies are in contact).
- (c)1 and 2 only — This drops statement 3, but 3 is true — contact forces such as drag and buoyancy act between a solid and a fluid, not only between two solids.
Forces are classified as contact forces (needing physical touch: normal reaction, friction, tension, spring/applied force, and fluid forces like drag and buoyancy) or non-contact/field forces (acting at a distance: gravitational, electrostatic, magnetic). Newton's third law applies to every force of either class, so 'obeys the third law' is not a way to tell them apart.
The question tests whether you know that a contact force need not be solid-on-solid — a body in air or water still feels contact forces from the fluid. Statement 2 is a distractor designed to make you hesitate, but since the third law holds universally it cannot be the false one. Once you accept all three as true, only option (d) fits.
- Contact forces require physical contact: normal reaction, friction, tension, spring/applied, and fluid drag/buoyancy.
- Non-contact (field) forces act at a distance: gravity, electrostatic and magnetic forces.
- Newton's third law applies to ALL forces — contact and non-contact alike — as action-reaction pairs.
- A solid moving through a fluid feels contact forces (viscous drag, fluid friction) and buoyancy.
All three statements in the question are true, so the answer is 1, 2 and 3.
- Assuming a contact force can only act between two solids (fluids count too).
- Thinking only some forces obey Newton's third law — all of them do.
- Confusing 'contact force' with 'friction' alone; friction is just one example.
NDA asks you to classify forces as contact vs non-contact or to test which statements about a force type are true — anchor every answer to the touch/field distinction and to the universality of the third law.
No directly related past PYQ was found.
- practice — not a real PYQ
Which one of the following is a NON-contact (field) force?
- (a)Friction
- (b)Tension
- (c)Gravitational force
- (d)Normal reaction
Answer(c) Gravitational force — it acts at a distance without physical contact; the others all require contact.
- practice — not a real PYQ
The upward force that a fluid exerts on a solid immersed in it is called
- (a)Tension
- (b)Buoyant force
- (c)Magnetic force
- (d)Electrostatic force
Answer(b) Buoyant force — a contact force exerted by a fluid on an immersed solid (Archimedes' principle).