## anonymous 4 years ago Last question: A rock is thrown downward from an unknown height above the ground with an initial speed of 10 m/s. It strikes the ground 3.0 s later. Determine the initial height of the rock above the ground. Question 8 options: 1) 44 m 2) 14 m 3) 74 m 4) 30 m 5) 60 m

1. anonymous

I only have 2 min left on the clock

2. anonymous

I thought it would be (-10)(3.0)-1/2(9.8)(4.0) = 49

3. anonymous

but thats not an option

4. TuringTest

$h=v_0t+\frac1 2at^2$because we have defined down as positive here and it was thrown down initially

5. TuringTest

a=g=9.8

6. TuringTest

$h=v_0t+\frac1 2gt^2=10*3+\frac1 29.8*3^2\approx?$

7. anonymous

74.1?

8. TuringTest

$h=v_0t+\frac1 2gt^2=10*3+\frac1 29.8*3^2\approx74$yep

9. anonymous

Ah, that makes sense, Thanks man

10. TuringTest

no prob :D