Boating:

A 100kg man(standing on shore) wishes to start his journey in a 200kg row-boat (parked in the water near the shore) with good initial speed. What he does is this:
1)He heaves the boat forward (with great effort) providing it with 2 units speed.

2)Next, he sprints on the beach sand, and jumps into the boat (his running direction coincides with the boats motion), with a velocity 5 units.

What is the final speed of the boat??


You'll encounter similar questions in your JEE.

13 comments:

  1. akash rupelaNovember 15, 2010 at 6:51 AM

    is the answer 3?

    ReplyDelete
  2. AmitNovember 15, 2010 at 12:58 PM

    if friction is not there between man and boat then, velocity of boat=2.
    if sufficient friction that man stops relative to boat, then velocity of boat=3.
    (I have also assumed liquid is non-viscous)

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  3. Saksham GuptaNovember 15, 2010 at 8:22 PM

    3 units

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  4. AmitNovember 16, 2010 at 12:02 AM

    bhaiya, please tell why viscosity wont have effect on the velocity, wouldn't it try to stop the boat.

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  5. Pratik JainNovember 16, 2010 at 1:04 AM

    yes same here ....3

    ReplyDelete
  6. AmitNovember 16, 2010 at 11:29 AM

    Ok bhaiya, I have realised my mistake, though my mistake can be true somewhere else. Here it might be that impulse by viscous force is negligible.

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  7. ♥◘○µ╦┬░Γ╪╬└↑φΦ╫╛◙«½╣↔⌐☺♠♦♣◘○November 17, 2010 at 8:40 AM

    answer is 3

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  8. shaanNovember 17, 2010 at 10:33 PM

    it is too simple a question(ACC TO anuj bhaiya's level) for its answer to be 3.
    though by simple thinkng, i also got 3.

    but here , it is possible ki we might have to conserve momentum initially also when he pushes the boat, HENCE INITIAL SPEED OF BOAT = 2*300/200=3.

    NOW , FINAL SPEED = 11/3

    PLEASE CONFIRM..

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  9. akash rupelaNovember 18, 2010 at 12:15 PM

    yaar delhiite, i mean thik hai Anuj bhaiya asaan question nahi dete hai, but this doesnt mean u will think complex everytime

    question says HE HAS "PROVIDED" IT 2 units speed anyhow, so no use questioning that part

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  10. Tushar SinglaNovember 18, 2010 at 12:19 PM

    i also thnk ans is 3....

    But q says "providing it with 2 units speed" (1st point)....

    In that case...mom will have to be conserved intially as well....

    initially man nd boat both move with 2 m/s nd man comes to rest by applying force.....nw considering man + boat system boat's initial vel shall be 3 m/s....
    'delhiite' might be correct here....

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  11. shouryaNovember 18, 2010 at 12:37 PM

    i think that the boat will have have speed 2 even after the man jumps on it as there is nothing givn abt fricton bw man n boat in the question.

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  12. shaanNovember 18, 2010 at 3:28 PM

    This comment has been removed by the author.

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  13. AnujNovember 18, 2010 at 4:35 PM

    Answer is 3 units, by simple conservation of momentum. Forgive my language, if you thought the question was ambiguous. :P.

    ReplyDelete

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