Throwing a tennis ball

Question

Eli stands on the balcony of a tall building and throws a tennis ball straight up at a speed of 14 m/s. He releases the tennis ball at a height of 60m from the ground. In parts a through c, round your answer to the nearest hundredth. 

 

A) When does the tennis ball hit the ground?

B) When does the tennis ball pass the point from which it was released?

C) What is the maximum height reached by the ball?

Answer 1

I see that no one has answered your question yet. This is a common problem in physics and dynamics problems in engineering. 

 

a) The basic formula is y=v₀t-gt²/2

9.81m/sec² x t² - (14 m/sec x t) - 60m = 0

 

quadratic equation t= -b+/- √b²-4ac /2a

 

t= 14+- √(-14)² -4(4.905)(-60)/ 2(4.905) = 5.20 sec

 

b) y = v₀t - gt²/2

 

At max height H, V_y = 0

Vy² = V²_0y - 2g(y-y₀)

 

0=(14)² -2(9.81)(H-60)

 

H=70m

 

The ball would fall 10m from max height of 70m. set y=0 and H=10m

y=gt²/2+H, t = 1.42 sec.

 

 

Therefore, 5.2 - 1.42 = 3.77 sec