velocity help please

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dalasTR

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Sep 13, 2009
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Use a(t) = -32 ft/sec squared as the acceleration due to gravity. A ball is thrown vertically upward from the ground with an initial velocity of 56 ft/sec. For how many seconds will the ball be going upward?

I have no idea how to start this. I know the position equation, but I'm not sure if I need it. I have this: Maybe v(t) = -32t + 56 = 0 ????
If that is right, I'm still not sure what to do next...
 
dalasTR said:
Use a(t) = -32 ft/sec squared as the acceleration due to gravity. A ball is thrown vertically upward from the ground with an initial velocity of 56 ft/sec. For how many seconds will the ball be going upward?

I have no idea how to start this. I know the position equation, but I'm not sure if I need it. I have this: Maybe v(t) = -32t + 56 = 0 ????
If that is right, I'm still not sure what to do next...
Click to expand...

What is 't' in your equation?
 
dalasTR said:
I don't even know :/
Click to expand...

t is time.

v(t) = 56 - 32t gives the velocity 'v' at time 't', so at time t=2, the velocity is 56-64=-8 ft/s.

You are asked "For how many seconds will the ball be going upward?", in other words, "until what value of t will v(t) be positive?"

Can you work it out now?
 
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