# 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.

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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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