Collisions - Elastic vs. Inelastic

P.6D:

Elastic vs Inelastic Collisions

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Elastic Collisions

0:0-1:38

• Elastic: Objects remain separate from one another after the collision, both Kinetic and Momentum is CONSERVED

• Nearly elastic collisions loose some kinetic energy due to heat and sound.

• (m1v1i + m2v2i)= (m1v1f + m2v2f)

InElastic Collisions

1:38-5:14

• InElastic: Objects remain together as ONE MASS.

• KINETIC ENERGY IS NOT conserved.

• We loose some KE to heat or sound

• Ptot=(m1v1i + m2v2i) BEFORE

• Ptot=(m1+m2)vf AFTER

Multiple Choice

Which equation should we use to predict the velocity of the two cars when they collide and stick to each other?

• $$P_{tot}=\left(m_1v_1\right)+\left(m_2v_2\right)$$  

• $$P_{tot\ }=\ \left(m1+m2\right)Vf$$  

Multiple Choice

Which equation should we use to predict the velocity of the two cars when they collide and move away from each other?

• $$P_{tot}=\left(m_1v_1\right)+\left(m_2v_2\right)$$  

• $$P_{tot\ }=\ \left(m1+m2\right)Vf$$  

Multiple Choice

(04:15) Comprehension Check: A 1300 kg car travels at 20 m/s and a 900 kg car moving at -15 m/s is moving head-on towards the first vehicle. When they collide, we consider it to be perfectly INELASTIC as they stick together and begin to slide to one side.

Calculate the speed and direction of the vehicles after impact. Remember to determine the total momentum before they collide.

• 25,115 m/s

• 885 m/s

• 26,000 m/s

• 11.42 m/s