[BMWPower06]

Yet another problems got me stumped, feel free to help:
Problem 1:
It takes 2.70 s for a small ball with a mass of 0.050 kg released from rest from a tall building to reach the ground. Calculate the height from which the ball is released.

If that ball had been released from the same height, but this time above the surface of the moon, how long would it have taken for the ball to hit the ground?


Problem 2:
Felipe is going for a physical before joining the swim team. He is concerned about his weight, so he carries his scale into the elevator to check his weight while heading to the doctor's office on the 21st floor of the building. If his scale reads 834 N while the elevator has an upward acceleration of 2.26 m/s2, what does the nurse measure his weight to be?

any ideas?

[rwwong]

Maybe it's time for a tutor!?

[schneid4323]

1. D=RT (Somewhere arround 9.8 is your acceleration and you have the time)

2. Get someone else to do it for you screw that. http://www.collegeboard.com/prod_dow...quationtab.pdf

That may help you, its every physics equation, all the problems you have asked are just dirivitives.

[boymonkey]

1:
35.7m
What's gravity on the moon??

2:
69.2kg

[Coldintake]

Originally Posted by boymonkey

1:
35.7m
What's gravity on the moon??

2:
69.2kg

1/6 of earth, last I remember. Gawd I hate mechanics.

[561design]

Originally Posted by rwwong

Maybe it's time for a tutor!?

LOL, what's he going to do when he has an exam and he can't access the internet. Or have 24 hours for other people to answer it for him. OH NOES!

[Ryan@Motorwerks]

1a. .5(acceleration)(time)=(.5)(9.8)(2.70)=13.23 meters
edit: I got this because the area(under the line) of the velocity v. time graph equals the distance displaced. So the area is the time*final velocity(since velocity is increasing constantly, final velocity equals time*acceleration)*(1/2)(because the graph is a triangle and the area of a triangle is 1/2bh)
1b. 13.23=.5(acceleration)(time)=13.23/(.5*(9.8/6)=16.2 seconds

2. (834*9.8)/12.06=678N=69.2kg

[Ryan@Motorwerks]

Originally Posted by boymonkey

1:
35.7m
What's gravity on the moon??

2:
69.2kg

how did you get that for #1????

[Josh49]

Originally Posted by 561design

LOL, what's he going to do when he has an exam and he can't access the internet. Or have 24 hours for other people to answer it for him. OH NOES!

Yeah we should probably explain stuff instead of just giving him answers..

[boymonkey]

Originally Posted by 335e90

how did you get that for #1????

v = a*t + v(initial)
v(average) = 0.5 * (v - v(initial)); our v(initial) = 0

get rid of v(initial) since it's zero, and plug in v from first equation
v(average) = 0.5 * (a*t)
d = v(average) * t = 0.5 * a * t^2

put in numbers and solve for unknown

[Neurorad]

Always start every answer by writing down the right equation.

You lose credit if you don't show all your work.

I hated that, teachers that bust your balls, even if you have the right answer.

[Josh49]

Originally Posted by Neurorad

Always start every answer by writing down the right equation.

You lose credit if you don't show all your work.

I hated that, teachers that bust your balls, even if you have the right answer.

Yep. And draw the Free-body-diagrams!! They make these questions much, much simpler..

In school, a lot of proofs and questions were several pages of math. If everything was right, but the very last calculation you messed up on, you could still get most the credit for that problem. So I guess it's worth the work to write it all down. It also maps out what you were thinking at the time, so they would know that conceptually you knew what was going on..

PITA, but getting the points are good vs. having the wrong answer and not getting any..

[SoYank]

RTFPB

[e92phreak]

Dam... I haven't touched this stuff in 20 years LOL... Is Halliday & Resnick still the college Physics book of choice? I had an answer book LOL...