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NEET & JEE · Physics, Chemistry, Maths, Biology

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Para is an AI research agent for NEET and JEE — Physics, Chemistry, Maths and Biology. Send it a question — typed, photographed, or as a voice note — and get a proper worked solution back in the same chat. No app, no login.

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Can't figure out this rod one

Angular momentum about the hinge is conserved through the collision — that's the whole trick.

m·v·(L/2) = I·ω I = ML²/3 + m(L/2)² M = 2m → ω = 6v / 7L
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What it can do

Solves it properly

Full working, step by step — not just a final answer.

Reads your photo

Point your camera at a module page, a test paper, or your own handwriting.

Understands voice notes

English, Hindi or Hinglish. It'll reply as a voice note too.

Works in your batch group

Ask in the group and everyone gets the answer, not just you.

Builds a page for hard ones

Complex questions get a full explainer page with diagrams you can play with.

Points out the trap

Tells you the mistake most students make on that exact question.

In the batch group

One student asks in Hinglish, as a voice note. Para answers the group — and flags the mistake most of them were about to make.

Batch 2027 · Doubts 48 members
▶ 0:14

Concave mirror wala — image real hai, so v is negative. Sign convention se shuru karte hain.

▶ 0:38

the trap

Most of the class keeps u positive here. It isn't.

How it works

01

Send the question

Text, photo or voice, in a chat or your group.

02

Get the answer

Worked solution in the thread, in seconds.

03

Go deeper if you want

Hard questions come with a live explainer page.

Hard questions get their own page.

Some questions need more than a chat message. Para builds a page for those — the full derivation, a diagram you can drag around, the common wrong turns, and a few practice variants. It stays up, so you can come back to it.

Open an example page →

para.page/rotational-collision-hinge Rotational motion JEE Main 2023 · Shift 2 A particle strikes a hinged rod at its midpoint. Find the angular velocity just after impact. Derivation 01 Torque about the hinge from the impulse is zero, so L is conserved. 02 Before impact, only the particle carries angular momentum. L₀ = m·v·(L/2) 03 After impact both rotate together about the hinge. I = ML²/3 + m(L/2)² 04 Set L₀ = Iω and substitute M = 2m. ω = 6v / 7L Diagram · drag the impact point rod · M, L m, v ω x / L 0.50 Common wrong turn Using linear momentum conservation. The hinge exerts an external impulse, so p isn't conserved — only L about the hinge is. Variant · strikes at L Variant · elastic Variant · find loss in KE

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