Proj Motion EX 5

Helena Dedic

A tennis ball is served at a height of 2.4 m at 30 m/s in the horizontal direction. The net is 0.9 m high at a horizontal distance of 12 m. Does the ball clear the net? If so, by how much? If not, where does it strike the net? < br>br>

Solution:

Knowing that the ball travels a horizontal distance of 12 m to the net, and knowing the initial velocity, we can calculate the time it takes from eq'n 1:

$\mathrm{\Delta }x=v_{xo}t$ 

$t=\mathrm{\Delta }x/v_{xo}$ 

t = 12 m / 30 m/s = 0.4 s 

$\mathrm{\Delta }y=v_{yo}t-4.9m/s^2{t}^2$ 

$\mathrm{\Delta }y=0-4.9m/s^2(0.4s{)}^2$ 

$\mathrm{\Delta }y=-0.784m$ 

y = 2.4 m - 0.784 m = 1.616 m 

The tennis ball clears the net!!

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