momentum and collision

- anonymous

momentum and collision

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- anonymous

Is it an elastic collision or an inelastic collision ??

- anonymous

it doesn't state that

- anonymous

So the question cant be answered because coefficient of restitution should be known to find the type of collision

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## More answers

- anonymous

it says head on collision

- anonymous

Head on means the axis on collision are at zero degree to each other. U can assume it to be elastic as far i feel like.

- anonymous

alright lets solve it that way

- anonymous

Hey check the question . North n East are at 90 degree. Its gonna be an in elastic collision then

- anonymous

sorry it is west and east i didnt notice at the directions while wiritng

- anonymous

Then assume it to be elastic n single axis collision.

- anonymous

ok so how do we solve it

- Jack1

|dw:1378719031169:dw|

- Jack1

p = momentum
m = mass
v = velocity
p = mv
so p truck (before collision) = ?
and p car (before collision) = ?

- anonymous

|dw:1378719256892:dw|

- anonymous

M1U1 + M2U2 = (M1+M2)V
M1, M2, U1,U2 are given in question. Substitute to find V

- Jack1

cool so p before = p after if we're assuming an elastic collision (conservation of momentum)
does it state whether the truch and car stick together?

- anonymous

That is not written

- anonymous

hey guys in the textbook ot is conservation of momentum
i have no idea about rest part

- anonymous

I wrote the conservation of momentum formula above

- Jack1

cool dude, so assume a merging of the mass after collision
and use @frnd 's formula above: m1 u1 + m2 ... etc
solve for v
u is initial speed of each respectively

- anonymous

whats u textbook has p total = p1 + p2 + p3 + ....+pn

- Jack1

?

- Jack1

p = mv
so all textbooks dealing with conservation of momentum

- anonymous

whats u in the formula frnd provided ? textbook has p_total = p_1 + p_2 + p_3 + ....+p_n...p is vector

- Jack1

ignore the textbook then, this question is alot simpler so use what's easy
the classic equation for conservation of momentum in an elastic collision is
M1U1 + M2U2 = (M1+M2)V
M1 = mass of truck,
M2 = mass of car,
U1 = speed of truck
U2 = speed of car
vector analysis only comes into this equation to the extent that as they're travelling in exactly opposite directions, make one of the directions the reference point, ie the truck, and therefore make the other direction negative, therefore speed of car = -150 mph
= -67.1 m/s Substitute to find V

- Jack1

|dw:1378720567315:dw|

- anonymous

181050=4500v
v=40.233

- anonymous

i think v has units too right @Jack1

- Jack1

sorry dude, did u remember to use negative 67.056 as your value for u2?
and v is in m/s, velocity has both magnitude and direction so remember to give it the appropriate direction based on positive or negative answer

- anonymous

oops

- Jack1

|dw:1378721164974:dw|

- anonymous

v = -4.5 some units

- Jack1

yep, i got -4.74, rounded up to sig figs is -4.7 meters/second , and as its negative we know it's moving west (as east was our reference direction)
so v= 4.7m/s west after collision

- anonymous

yep....so wait what did we just find @Jack1

- Jack1

the car and the truck crash together
they have different masses, speeds and directions before the crash
they merge together because of the crash
the new joined mass has a velocity of 4.7m/s west after the crash
you can put this in terms of momentum if you wish (mass of wreck = 4500...assuming kgs?)
momentum of wreck = 20, 117 west

- anonymous

last confusion where did you get 20, 117 from

- Jack1

momentum units kg . m/s (assuming your weights are in kgs?)

- anonymous

ya mass is in kg

- Jack1

21,117 by not rounding
if you go 4.7*4500 = 21,150
but use:
a*b + c*d = (a+c)V,
a = 3000, c = 1500, b = (60*0.44704), d = (-150*0.44704)
note: 1 mph = 0.44704 m/s
then gives you momentum of 20,116.8 kg . m/s
then rounding = 20,117

- anonymous

ty so much helped a lot

- anonymous

waht r the units again

- Jack1

all good dude, always welcome hey, sing out if you need clarification on anything
if not, slaters ;)

- anonymous

lol, this stuff is so easy! [:

- Jack1

of momentum: kg . m/s
of velocity: meters/second
of mass: kg

- anonymous

its fine dude, we r frnds @Jack1 thats why she was bragging it

- Jack1

ah, nvmd, my bad ;{

- anonymous

u good ... thx for explaining stuff

- Jack1

yw, cya

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