Say there's a ball being thrown upwards (from the bottom to the top of a building) with an initial speed of 29.4 m/s for 4 seconds at an acceleration of -9.8 m/s².(adsbygoogle = window.adsbygoogle || []).push({});

Now here's a few of my problems:

1.) My book says the ball would stop after 3 seconds. Wouldn't it therefore be pointless to calculate what would happen in 4 seconds?

2.) My book says the end speed (V1/Vf) would be -9.8 m/s. Doesn't the end speed always equal acceleration times time (V1 = at) which would therefore be -39.2 m/s?

Also, what's the difference between starting at rest (with the initial speed being zero) and being thrown (for example, in this case, 29.4 m/s), isn't gravity technically 'throwing' the object in question?

Thanks to anyone who can explain this, it's confusing me alot. I've only been working with physics (self-teaching) for about 4 days so excuse the newbieness of the question.

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# Homework Help: Some quite confusing problems

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