|
 |
|
|
|
|
 The momentum, p, of an object of mass m is
p =mv
Momentum has SI units of Kg m/s or Ns. Bothunits are absolutely equivalent and correct. Hence
1 Kg m/s = 1 Ns
Conservation of momentum:
The total momentum of a system of objects always remain constant, as long as no other force acts on thay system of objects.
Eg...
A stationairy -238 uranium nucleus emits an alpha particle, namely helium -4 nucleus at 1.4 x 10 ^7 m/s. Calculate the recoil speed of the daughter nucleus, throium - 234. Take 1 u = 1.67 x 10 ^ -27 kg.
The example is broken down into three stages.
Draw a diagram, my teachers are always telling me how much diagrams help, guess the book just emphasises that they were right.
Next Write down what you're given and then
mass of alpha particle = m = 4u;
mass of thorium -234 =M = 234u
recoil speed of throium -234 = V;
speed of alpha particle = v = 1.4 x 10^7
Use the law described above.
momentum after emission = momentum before emission
Since the uranium is at rest its momentum before emission is zero, so
momentum after emission = mv+ MV = 0
V= -mv/M = -(4u x 1.4 x 10^7 m/s)/(234u) = 2.4 x 10^5 m/s
Momentum is a vector quantity, i.e has both magnitude and direction, so if an event occurs in two or three dimensions then we might have to solve by using components or making a scale drawing. I say using components is easier because it ties in with my Mechanics module so just more practice. I'll go through components in a different post. Right now i just wanna do some more questions.
1) A ball of mass 100g is travelling at 25 m/s. What is its momentum in kg m/s...
p=mv
100g to kg -----> 100/1000 x 25 = 2.5 Kg m/s.
2) Show that 1kg m/s is equivalent to 1 Ns.
f=ma, a force of 1 N accelerate a mass of 1kg by 1 m/s^2 so 1 N= 1kg ms^2. Therefore 1 Ns = 1 kg ms^-2 x 1s = 1kg m/s...
|
|
|
|
|
|
 The most significant of the many reasons i have for starting to use a blog as revision is that
Over the past couple years about 2 to 3, I have seen myself become more addicted to the computer and the internet. I've become so fascinated that within those three years I've become some what proefficient with quite a few programming languages, including ASP.NET, VB and ofcourse PHP. While i don't see this being a bad thing in itself the more worrying fact is that while my knowledge grew it was not targeted at the things it should be such as school. As a result I've seen grades become prograssively worse. From a promising A* student down to D's and god knows what else. Since it is starting to seem very hard to break this "obsession with the net" I've decided to use it to my advantage to get my grades back up. Unfortunately i have no one standing over my shoulder with a whip telling me to crack on with coursework and revision, i never have and i always did well so i suppose they've come to think that i am responsible enoough to take charge of my own learning. Yeah, they believe because "its courtney" it will all work out fine, except for one teacher who really annoys me but there was some element of truth in what he said.
No Mr B, I don't believe in miracles either and i know if i don't work i won't get the grades i need. Actually i take that back, i do believe in miracles, i just know i won't get the grades i want without the work that it entails.
What i intend to do is go over all the work i do through the day at least once, rewrite it in my own words where i can and hopefully remember it all. Ofcourse i will have to get some stuff from the text books so if any text books writers happen to come cross my blogs, please don't sue me :( or any of that other legal crap either. I'm only trying to pass the bloody course. If there is some content you want off because its yours let me know before you send the coppers knocking on my door. I have no intention of doing any of that copyright infringement stuff ok?
For anyone else thats just looking for certain answers and happen to come accross my blog, please double check any answers etc i post. Yeah i'm getting some of it from the books but things do go wrong. For those of you who are just here because you love me that much, don't turn it into an obssession alright.... I've got grades to boost lol.
On a serious note though, i hope this helps me and anyone else of interest.
|
|
|
|
|
|
Favorites
Del.icio.us
Digg
Furl
Magnolia
StumbleUpon
Google
Yahoo
Technorati
BlinkList