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# Help me with two easy physics questions please

Registered User Posts: 621 Member
edited September 2005
Hey guys my physics homework is due on 9/12 and I need help on these two problems.

1. How long is Tina, a ballerina, in the air when she leaps straight up with a speed of 1.8m/s

2. A Christmas tree ball will break if dropped on a hardwood floor with a speed of 2.0 m/s or more. Holly is decorating her Christmas tree when her cat Trickor, taps a ball, causing it to fall 15 cm from a tree branch to the floor. Does the ball break?

I know that there has to be an easy formula for this but I can't find it. If you can tell me the process by which you get the answer I would be very grateful.
Post edited by pilebay on

## Replies to: Help me with two easy physics questions please

• Registered User Posts: 621 Member
I know someone out there knows how to do this. I keep reading about people on this site that get 800's on the SAT II Physics. These questions are really driving me crazy I really really need help.
• Registered User Posts: 1,847 Senior Member
I'm really awful at this, but I'll try:

vi= initial velocity (m/s)
vf= final velocity (m/s)
a= acceleration (m/s^2)
t= time (seconds)

1) For the time going up:
a = (vf-vi)/t
-9.8 = (0 - 1.8)/t
t = 1.8/9.8 = .18, double because she comes down: .367 s

2) d= (vf^2 - vi^2)/2a
.15 = (vf^2 - 0)/2(9.8)
2.94 = vf^2
vf = 1.71 m/s: the ball does not break

Big Five equations rock.
• Registered User Posts: 2,217 Senior Member
a) use the equation v(final) = v(initial) + a*t
For the time going up
0 = 1.8 + -9.8*t
t=.183
Multiply by two to get total time in the air: .183 * 2 = .367s

tkm is right for the second one
• Registered User Posts: 621 Member
Thanks so much! I really suck at Physics so I am sure that there will be a lot of posts from me in the coming year.
This discussion has been closed.