You are here:
Careers: Physics/physics
Advertisement
Question
QUESTION: A ball of mass 0.120 kg is dropped from rest from a height of 1.25 m. It rebounds from the floor to reach a height of 0.600 m. What impulse was given to the ball by the floor?
ANSWER: Hi Will,
the impulse given must be equal to the sum of impulse to stop the ball (mv_drop) and the impulse necessary for the rebound (mv_up). Speed v_drop just before the ball touches the ground (while h1=0.5*g*t1^2) is
v_drop=g*t1=g*sqrt(2*h1/g)=sqrt(2*g*h1).
Speed v_up just after the ball looses contact with the floor is
v_up=g*t2=g*sqrt(2*g*h2)
So the impulse given by the floor is p=m*[sqrt(2*g*h1)+sqrt(2*g*h2)]. You do the numbers :-).
You are welcome, I hope it helps.
Daniel
---------- FOLLOW-UP ----------
QUESTION: sorry, but i'm a little confused about your symbols. And how did you get h1 to be .5*g*t1^2
Hi,
h1=1.25m, h2=0.600m ('h' stands for 'height'), g=9.81m/s^2, m=0.600kg
You never said, where the ball was dropped, so I assumed it was on Earth (hence the value of acceleration 'g'). Time is t1 for drop, t2 for rise and it is the standard notation. h=(1/2)*g*t^2 is the elementary equation of uniformly accelerated motion in the gravitational field on Earth. It is the same for motion down and up, but for the reasons behind I must direct you to some elementary physics textbook. The laws of motion are not complicated, but one needs to learn them systematically so that there is no undue confusion about them.
Good luck.
Daniel
Related Articles
- A to Z Index
- Humor at The Mining Co. Daily Surprise! - Milk: Where's Your Moustache - The MikeDurrett Show - 02/25/99 - Humor
- Molarity Example Problem - Worked Chemistry Problems
- Smoking Makes Multiple Sclerosis Worse - Smoking Speeds MS Progression
- Cat Breed Profiles A to Z - Breeds beginning with G
Daniel Mazur
Expertise
Questions anyone (teenager, undergrad, graduate, professional) may ask on physics, mathematics or inorganic chemistry. Questions may concern subjects themselves or a possible future career in them, if you need advice on a school or hobby project, or you just came across a question that is beyond your current curriculum. I answer bare textbook problems sometimes, but I reserve the the right to redirect you to Physics-Physics section. The kind of questions I like to answer: I just started having science classes at school and they seem difficult, but I enjoy them. Where do I find more information on this, which is not in textbooks but still comprehensible to me? Just leaving high school, and I feel science is really the thing for me. Can you recommend a school and an undergrad program suitable to my inclinations? I am in my second undergraduate year in Physics. We learned the basics of universe expanding this year, the Hubble constant and all that, but invited speakers that gave talks on astrophysics in our department seemed not to agree with this model at all. Is it of any use at all? I am building a [materials research] experimental device for my masters/doctorate thesis and I have the following problem:... I have tried ..., but it still doesn't work. Where might the problem be?
©2012 About.com, a part of The New York Times Company. All rights reserved.