Calculus/physics problem?

So my calculus teacher decided to give us some physics problems and I have no what idea what I'm doing. Some answers would be nice and also explainations to go with them. 1. An object is dropped from a building 100 meters tall. When is the object halfway down the building? My answer is 3.19 seconds but I... show more So my calculus teacher decided to give us some physics problems and I have no what idea what I'm doing. Some answers would be nice and also explainations to go with them.

1. An object is dropped from a building 100 meters tall. When is the object halfway down the building? My answer is 3.19 seconds but I don't know if thats right.
2. Standing on the ground, I toss an object upward with a velocity of 15m/sec. When does it reach its highest point?
3.Standin gon a building 100 meters tall, I toss an object upward with a velocity of 15m/sec. What is its height after 3 seconds?
4.Standing on a building 100 meters tall, I toss an object upward with a velocity of 15m/sec. When does it hit the ground?
5.Standing on a building 100 meters tall, I toss an object downward with a velocity of 15m/sec. How fast is it going when it hits the ground?
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