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

Question

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

anonymous · Answer

I only have 2 min left on the clock

anonymous · Answer

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

anonymous · Answer

but thats not an option

turingtest · Answer

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

turingtest · Answer

a=g=9.8

turingtest · Answer

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

anonymous · Answer

74.1?

turingtest · Answer

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

anonymous · Answer

Ah, that makes sense, 
Thanks man

turingtest · Answer

no prob :D