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NEET-XII-Physics

P1 year:2019

with Solutions - page 2
Qstn# 29 Prvs-QstnNext-Qstn
  • #29
    The work done to raise a mass m from the
    surface of the earth to a height h, which is
    equal to the radius of the earth, is:
    (1) mgR
    (2) 2mgR
    (3) ½mgR
    (4)``\frac32``mgR
    digAnsr:   3
    Ans : ( 3 )
    Sol.
    h = R
    RM
    Initial potential energy at earths surface is
    =
    i
    GMm
    U
    R
    Final potential energy at height h = R
    =
    f
    GMm
    U
    2R
    As work done = Change in PE
    ∴ W = U
    f
    - U
    i
    = = =
    2
    GMm gR m mgR
    2R 2R 2
    (∵GM = gR
    2)