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Physics university

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In a tennis match, a player wins a point by hitting the ball sharply to the ground on the opponent's side of the net.

If the ball bounces upward from the ground with a speed of 17 m/s , and is caught by a fan in the stands with a speed of 12 m/s , how high above the court is the fan? Ignore air resistance.


Explain why it is not necessary to know the mass of the tennis ball.

  • Physics university -

    the total energy is the same.

    PE + KE= constant
    mgh+ 1/2 mv^2=constant

    now when h is zero(at the ground) v is 17m/s
    so term one mgh and term 2 KE act in opposite direction (when one goes up 10, the other goes down 10)
    Since velocity was given, it is not necessary to know mass.

  • Physics university -

    ugh confused

  • Physics university -

    PE1 + KE1 = PE2 + KE2
    mgh1 + mv12/2 = mgh2 + mv22/2
    m(gh1 + v12/2 ) = m(gh2 + v22/2 )
    gh1 + v12/2 = gh2 + v22/2
    but h1 = zero so

    ½(16)2 = 9.81h + ½(12)2
    128 = 9.81h + 72
    h= 5.7 m

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