Question 4
Remark
You should know how to do this after I tell you the secret. It does not matter which way you do this after you make your first decision and even that will give you the same answer. I think I'll explain this in the givens.
Givens
You have to make up your mind which way is positive and which way was negative. You have two choices. Both will work. But you must be consistent.
I'm going to take up as positive because the direction is consistent with the x,y grid or axis. y going up to me is plus.
The balloon is rising constantly with a speed of 5 m/s. When you drop something from something flying upwards, gravity immediately says "Whatever goes up is going to come down. I am the law of up and down."
vi = + 5 m/s
a = - 9.81 m/s^2
t = 0.25
d = ??? (You want the position)
Equation
Here's the key part. What equation are you going to pick? There's only one that will relate d,t,a,vi. Which one?
If you said d =(vf + vi)*t/2, you would be wrong. You don't care about vf.
d = vi*t + 1/2a*t^2 is the correct answer.
Solve
d = 5*0.25 + 1/2* (- 9.81) * (0.25)^2
d = 1.25 - 1/2 * 9.81 * 0.0625
d = 1.25 - 0.9434
d = 0.3065 meters in the plus direction
Comment
But what does that mean? It means that at the starting position which is 40 meters above the ground, you are 0.3065 meters above that starting point. Since you are asked for the position of the sandbag, you are 40 meters + 0.3065 meters above the earth's surface or 40.3065 is the position.
Problem 6
You should be able to do this by listing your givens and then include what you looking for. It is an application of one of the big four. The only trick is how far the egg will descend
The answer to that is d = 46 - 1.8 = 44.2 meters. There is nothing else that is tricky.
Givens
d = 44.2 meters
vi = 0 dropped always means vi = 0
a = 9.81
t = ???
Equation
Which one of the big 4 is it? Now solve. You should get an answer close to 3. Be sure and round.
The answer shouldn't be a.
Problem 8
You should be able to do this on your own. Write down the givens and what you want. Pick one of the big 5 equations. v <> 0, but both vi and a are going in the same direction: everything should be fine.
Problem 7
This is like the hot air balloon. Your givens will tell you which equation should be used. I'll write the givens for you.
Givens.
vi = 12 m/s
a = - 9.81
d = 60.0 This is going upward from ground level it's plus.
vf = ?
Equation
?
Comment.
You can avoid all the teaching just be reposting the question somewhere else, but I really think you ought to try these before doing that. At some point someone will make you do all this. You've got good instructors here. Make use of them.
