The figure given below shows the direction of the two forces P and Q acting on a skydiver : Which one among the following statements is correct about the two forces ?

Q: What is the answer to NDA (II) 2024 GAT Q125?

C. Correct — C. In the printed figure the arrow labelled **Q points upwards** and the arrow labelled **P points downwards**. So P is the skydiver's weight and Q is the air resistance opposing the fall. Opening the parachute changes exactly one of them. The **weight P depends only on mass and gravity**, neither of which the parachute alters, so P stays the same. The **drag Q depends on the area presented to the air**, and the canopy multiplies that area many times over, so Q increases sharply — which is why the skydiver decelerates. That is statement (c): P unchanged, Q increased. (Provisional — pending the official UPSC key.)

(a)Force P is caused by the gravity and force Q is caused by the friction
(b)When the force P is bigger than the force Q, the speed of the skydiver remains the same
(c)After the parachute opens, force P remains the same while force Q increases
(d)After the parachute opens, force P decreases while force Q increases

Answer

Why

Correct — C. In the printed figure the arrow labelled Q points upwards and the arrow labelled P points downwards. So P is the skydiver's weight and Q is the air resistance opposing the fall.

Opening the parachute changes exactly one of them. The weight P depends only on mass and gravity, neither of which the parachute alters, so P stays the same. The drag Q depends on the area presented to the air, and the canopy multiplies that area many times over, so Q increases sharply — which is why the skydiver decelerates.

That is statement (c): P unchanged, Q increased.

Why the others are wrong

(a)
Force P is caused by the gravity and force Q is caused by the friction — The first half is right and the second is only loosely so. Q is air resistance, and although school texts often group air resistance under friction, the drag on a skydiver comes mainly from the pressure difference across the body, not from frictional rubbing. Statement (c) is exactly true, which makes it the better answer.
(b)
When the force P is bigger than the force Q, the speed of the skydiver remains the same — If the downward weight exceeds the upward drag there is a net downward force, so by Newton's second law the skydiver accelerates and the speed INCREASES. Constant speed requires P and Q to be equal, which is the terminal-velocity condition.
(d)
After the parachute opens, force P decreases while force Q increases — Q does increase, but P cannot decrease. Weight is mass times gravitational field strength, and opening a parachute changes neither.

Concept

A falling body carries a constant downward weight and an upward drag that grows with speed and with the area presented to the airflow. While weight exceeds drag the body accelerates; when they become equal the net force is zero and the body falls at a constant terminal velocity. Deploying a parachute raises the drag abruptly, so the body decelerates until a new, much lower terminal velocity is reached.

Identify which arrow is which before reading the statements — the upward arrow can only be the resistive force. Then test each statement against a single principle: weight is fixed, drag is not. That disposes of (d) at once and exposes (b) as a misstatement of Newton's second law. Option (a) is the interesting one: it is close enough to be tempting, and it is worth knowing that examiners treat 'air resistance' and 'friction' as distinct when a more precise statement is available.

Key facts

P points down and is the weight; Q points up and is air resistance.
Weight depends on mass and g, so a parachute does not change it.
Drag depends on speed and on the area facing the airflow.
Constant speed requires P = Q — terminal velocity.
P greater than Q means acceleration, not constant speed.

What the parachute changes

P — weight, downward→Unchanged: mass and g are unaffected

Q — air resistance, upward→Increases sharply: the canopy presents a far larger area

Result→Q briefly exceeds P, so the skydiver decelerates

If P were bigger than Q→Net downward force — speed rises, it does not stay constant

Only the drag changes when the canopy opens — statement (c).

Study next

Terminal velocity and the balance of weight against dragNewton's second law applied to falling bodiesFactors affecting air resistanceFree-body diagrams for a parachutist

Common traps

Thinking the weight changes when the parachute opens.
Reading 'P bigger than Q' as a constant-speed condition instead of an accelerating one.
Settling for the loosely worded option when an exactly true one is present.

NDA prints a labelled force diagram and offers statements about the forces — fix which arrow is which, then test each statement against what can and cannot change.

Related PYQs

NDA_GAT_2024_II_Q702024Open & attempt →

Which one among the following diagrams may correctly represent the motion of a skydiver during a jump?

(a) Diagram (a)
(b) Diagram (b)
(c) Diagram (c)
(d) Diagram (d)

Answer(a) Diagram (a)

The same jump seen as a speed-time graph rather than a force diagram — the plateau is where P and Q balance, and the abrupt drop is the moment Q jumps while P stays put.

Practice

practice — not a real PYQ
A skydiver falls at constant velocity. This means that
- (a)the weight is greater than the air resistance
- (b)the air resistance is greater than the weight
- (c)the weight and the air resistance are equal
- (d)there is no air resistance
Answer(c) the weight and the air resistance are equal — the net force is zero, so the speed does not change.
practice — not a real PYQ
Immediately after a parachute opens, the skydiver's acceleration is
- (a)downward and equal to g
- (b)upward, so the speed decreases
- (c)zero
- (d)downward, so the speed increases
Answer(b) upward, so the speed decreases — drag momentarily exceeds the weight.