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# PH 121 9.5-9.6

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## Richard Datwyler

on 21 June 2018

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#### Transcript of PH 121 9.5-9.6

Explosions and 2 Dimensions
An explosion is the opposite of a collision.
Maybe a bit better, it is the opposite of an
inelastic collision.

Instead of a few masses sticking together into
one mass
It is one mass breaking apart into many masses.
Again if the system is isolated,
(no external forces)
then the momentum will be conserved.

This is true even though there is an
extremely large force when it explodes.
because this force is an internal one.
http://media.pearsoncmg.com/aw/aw_0media_physics/vtd/video16.html
In most explosions, the initial momentum is zero
so because momentum is conserved the final momentum
must be zero too.
If the problem is linear, and there are just 2 objects, then
the two momentum are equal and opposite.
Demo
Momentum in multiple dimensions
Well, what can we say, momentum is a vector quantity, thus it can be broken down into parts.
If the total momentum is conserved,
each component will be too.
A firecracker in a coconut blows the coconut into 3 pieces. Two pieces of equal mass fly off south and west, perpendicular to each other at a speed of v. The third piece has twice the mass as the other two.what are the speed and direction of the third piece?
A 75 kg shell is fired with an initial speed of 125 m/s at an angle of 55 degrees above the horizontal. Air resistance is negligible. At its highest point, the shell explodes into two fragments, on four times more massive than the other. The heavier fragment lands directly below the point of the explosion. If the explosion exerts forces only in the horizontal direction, how far from the launch point does the lighter fragment land?
An object at rest on a flat, horizontal surface explodes into two fragments, one seven times as massive as the other. The heavier fragment slides 8.2 m before stopping. how far does the lighter fragment slide? assume both fragments have the same coefficient of kinetic friction.
402 m
4495 m
.707 v at 45 degrees
A 20 gram clay ball traveling 2.0 m/s north, a 30 gram clay ball traveling west at 3.0 m/s and a 40 gram clay ball traveling south east (45 degrees) at 4.0 m/s all collide and stick together at the same time.
What is the speed and direction of the resulting blob of clay?
.852 m/s
72.4 degrees below x axis
A 2100 kg truck is traveling east through an intersection at 2.0 m/s when it is hit simultaneously from the side and the rear. Once car is 1200 kg traveling north at 5.0 m/s. The other is a 1500 kg traveling east at 10 m/s. The three slide as one body after the collision. What are their speed and direction just after the collision?
4.19 m/s
17.4 degrees north of east
A 20 kg wood ball hangs from a 2.0 m long wire. The maximum tension the wire can withstand without breaking is 400 N. A 1.0 kg projectile traveling horizontally hits and embeds itself in the wood ball. What is the greatest speed this projectile can gave without causing the cable to break?
90.3 m/s
" which type of collision are explosions the opposite of."
"Once again the stop and think got me"
"Why does velocity play such a big role in momentum?
Could you go over example 9.9 in class?"
"could you go over momentum in two dimensions"
"Could you review how we determine an elastic vs inelastic collision?"
Full transcript