posted by Jessica on .
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.
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.
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