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# LPH 105 W15 7.4-6

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## Richard Datwyler

on 26 May 2016

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#### Transcript of LPH 105 W15 7.4-6

Elastic collisions
A 3.5 kg ball moving east with as speed of 13 m/s collides elastically with a 1.5 kg ball initially at rest.
What are the speeds of each ball after the collision?
5.2 m/s
18.2
Note the differences of the velocities before and after the collision.
A 2.5 kg ball collides linearly and elastically into a 4.0 kg ball. This second ball was initially at rest, but it is found to be moving with a speed of 4.9 m/s after the collision.
(a) what was the speed of the first ball, before and after the collision?
(b) what fraction of the initial kinetic energy was transferred into the stationary ball after the collision?
6.37 m/s & -1.47
94.7%
A 2.7 kg ball moving 7.2 m/s east collides with a 3.5 kg ball moving 5.3 m/s east elastically. What is the speed of each ball after the collision?
5.05 m/s & 6.95 m/s
inelastic
Car A hits car B (initially at rest and of equal mass) from behind while going 38 m/s. Immediately after the collision, car B moves forward at 15 m/s and car A is at rest.
What fraction of the initial kinetic energy is lost in the collision?

.844
a 35 gram bullet is shot at a speed of 250 m/s, it collides with and emerges out of the back of a 3.5 kg block of with a speed of 75 m/s.
(a) how fast is the block of wood moving? (assume frictionless surface)
(b) what fraction of initial KE was lost in this collision?
1.75 m/s
.905
"What difference does it make in how we set up equations when we are working with inelastic vs elastic collisions?"
"In inelastic collisions where does the energy go? -- Does some of it transfer to heat and the rest is kinetic over the two objects?"
"Where I am struggling currently is figuring out how to derive/substitute equations to match the current problem."
"I'm kind of confused on how to set up and solve these problems "
In an inelastic collision a 250 g chunk of clay initially moving at 15 m/s hits a 1.5 kg block of wood at rest, what is their speed after the collision, assume completely inelastic. (answer should look like '3.5 m/s')

7.2 - 5.3 = 1.9
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