Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
NDA 2026
Exam
NDA
Year
2026
Subject
General Ability
Chapter
General Science

NDA 2026 · General Ability · General Science

The position vector of a particle is given by r = 3 \,t^2 i + 2 \,t...

The position vector of a particle is given by r⃗=3 t2i^+2 tj^+5 k^\vec{r} = \sqrt{3}\,t^2\hat{i} + \sqrt{2}\,t\hat{j} + \sqrt{5}\,\hat{k}. Which one of the following statements is correct?

Options

  1. AThe force acting on the particle is parallel to the instantaneous momentum of the particle.
  2. BThe force acting on the particle is perpendicular to the instantaneous momentum of the particle.
  3. CThe particle experiences zero force.
  4. DThe force acting on the particle is not parallel to the instantaneous momentum of the particle.

Correct answer

D. The force acting on the particle is not parallel to the instantaneous momentum of the particle.

Step-by-step solution

Given position vector r⃗=3t2i^+2tj^+5k^\vec{r} = \sqrt{3}t^2\hat{i} + \sqrt{2}t\hat{j} + \sqrt{5}\hat{k}

Velocity v⃗=dr⃗dt=23ti^+2j^\vec{v} = \dfrac{d\vec{r}}{dt} = 2\sqrt{3}t\hat{i} + \sqrt{2}\hat{j}

Instantaneous momentum p⃗=mv⃗=m(23ti^+2j^)\vec{p} = m\vec{v} = m(2\sqrt{3}t\hat{i} + \sqrt{2}\hat{j})

Acceleration a⃗=dv⃗dt=23i^\vec{a} = \dfrac{d\vec{v}}{dt} = 2\sqrt{3}\hat{i}

Force F⃗=ma⃗=23mi^\vec{F} = m\vec{a} = 2\sqrt{3}m\hat{i}

Taking the cross product of force and momentum:

F⃗×p⃗=(23mi^)×m(23ti^+2j^)=26m2k^≠0\vec{F} \times \vec{p} = (2\sqrt{3}m\hat{i}) \times m(2\sqrt{3}t\hat{i} + \sqrt{2}\hat{j}) = 2\sqrt{6}m^2\hat{k} \neq 0

Since the cross product is non-zero, the force is not parallel to the instantaneous momentum.

Also, F⃗⋅p⃗=12m2t≠0\vec{F} \cdot \vec{p} = 12m^2t \neq 0, so they are not perpendicular either.

Answer: The force acting on the particle is not parallel to the instantaneous momentum of the particle.
Practice General Science on Quantrex Academy →

More from General Science

For an object in gravitational field, the gravitational potential is the same at two… NDA 2026A very large container consists of an ideal gas. The speed of sound in the gas is x .… NDA 2026A constant power machine pulls a block on a smooth horizontal surface. Which one of the… NDA 2026A ball is dropped from rest from height h above the ground in frame S (the Earth's… NDA 2026A pendulum of length L oscillates with an angular amplitude of θ = 60^ ^ ∘ and time… NDA 2026A solid of mass m has temperature-dependent specific heat as C(T) = C_0 + α T , where C_0… NDA 2026In a certain process, the relation between pressure (P) and volume (V) , for an ideal… NDA 2026An object is placed far beyond the centre of curvature of a concave mirror. The object… NDA 2026 Full General Science list All NDA PYQs