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Eddi Din [679]
3 years ago
8

H=255-21t-16t^2 PLEASE HELP!!

Mathematics
1 answer:
Colt1911 [192]3 years ago
4 0

Answer:

3.15 seconds is the answer.

<u>Explanation</u>

when the ball touches the ground, h =0

hence,

0=255-21t-16t²

16t²+21t-225=0

here a=16 ,b=21, c= -225

t=   \frac{ - b± \sqrt{ {b }^{2}  - 4ac} }{2a} \\  \\ t=   \frac{ - 21± \sqrt{ {21}^{2}  - 4 \times 16 \times  - 225} }{2 \times 16} \\  =  \frac{ - 21 ± \sqrt{441 - ( - 14400)} }{32} \\  =  \frac{ - 21± \sqrt{14841} }{32}  \\  =  \frac{ - 21±121.82}{32}  \\  \\ t =   \frac{ - 21 + 121.82}{32}  \: or \:  \: t =  \frac{ - 21 - 121.82}{32}  \\ t = 3.15 \:  \: or \:  \: t =  - 4.46

time cannot be negative, hence t = -4.46 can be avoided

The ball takes 3.15 seconds to hit the ground.

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