Which one among the following statements is correct?
- (a)Pressure has magnitude as well as direction
- (b)As we go deeper in a liquid, the pressure decreases
- (c)Action and reaction forces act on the same object
- (d)Pascal and N/m² represent the same unit
Correct — D, 'Pascal and N/m² represent the same unit'. Pressure is force per unit area, and its SI unit, the pascal (Pa), is defined as exactly one newton per square metre (1 Pa = 1 N/m²). The two are just different names for the same unit, so this statement is true.
- (a)Pressure has magnitude as well as direction — False — pressure is a scalar quantity. It has magnitude only; at a point in a fluid it acts equally in all directions, so it has no single direction of its own.
- (b)As we go deeper in a liquid, the pressure decreases — False — pressure increases with depth. The pressure due to a liquid column is P = hρg, which grows as the depth h increases because more liquid weighs down from above.
- (c)Action and reaction forces act on the same object — False — by Newton's third law, action and reaction act on two DIFFERENT objects. If they acted on the same body they would cancel and nothing could ever accelerate.
Pressure is the force acting per unit area, P = F/A, and is a scalar quantity. Its SI unit is the pascal (Pa), defined as one newton per square metre. In a liquid, pressure rises with depth as P = hρg, and Newton's third law pairs act on separate bodies.
This is a spot-the-true-statement item, so three options must be eliminated. Test each against a core fact: pressure is a scalar (not a vector), it grows with depth (not shrinks), and third-law pairs act on different bodies (not the same one). Only the unit equivalence survives.
- One pascal equals one newton per square metre (1 Pa = 1 N/m²).
- Pressure is a scalar; at a point in a fluid it acts equally in all directions.
- Liquid pressure increases with depth according to P = hρg.
- Newton's third-law action and reaction forces act on two different bodies, never on the same one.
- Pressure is a scalar — it has magnitude only, not direction.
- Action and reaction always act on different bodies, so they never cancel each other.
This appears as a 'which statement is correct' set that mixes a unit fact with common misconceptions about pressure and Newton's third law.
Which one of the following is a vector quantity?
- (a) Momentum
- (b) Pressure
- (c) Energy
- (d) Work
Answer(a) Momentum
Same concept behind option (a) — pressure is a scalar. UPSC's answer marks momentum as the vector and lists pressure, energy and work as scalars, confirming exactly why 'pressure has magnitude as well as direction' is the wrong statement here.
- practice — not a real PYQ
The SI unit of pressure, the pascal, is equivalent to
- (a)1 N·m
- (b)1 N/m²
- (c)1 kg/m³
- (d)1 J/s
Answer(b) 1 N/m² — one pascal is defined as one newton per square metre.
- practice — not a real PYQ
As a diver goes deeper into the sea, the water pressure on the diver
- (a)decreases
- (b)increases
- (c)stays the same
- (d)becomes zero
Answer(b) increases — pressure in a liquid rises with depth as P = hρg.