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a girl on a bridge throws a rock straight down at -12.5 m/s. it hits the ground 38.4 m below. How much time did it take?

Respuesta :

Answer:

Explanation:

Poster already has the right answer in comment above but the displacement should be -38.4m as it is below.

Using the kinematic equation: s = vt + 1/2at^2 and gravity at -9.8m/s^2

-38.4 = -12.5t + 1/2(-9.8)t^2

4.9t^2 + 12.5t -38.4 = 0

t = 1.80s or -4.35s

As time cannot be negative, the answer is 1.80s.
  • Initial velocity=u=12.5m/s
  • Distance=s=38.4m
  • Time be t

[tex]\\ \rm\rightarrowtail s=ut+\dfrac{1}{2}gt^2[/tex]

[tex]\\ \rm\rightarrowtail 38.4=12.5t+4.9t^2[/tex]

On solving further we get

  • t=1.8s

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