Impulse and Momentum: Find Common Velocity & Fraction of Kinetic Energy

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The discussion centers on a collision between a 1550kg car traveling at 12m/s and a stationary 1220kg car, resulting in both cars moving together post-collision. The common velocity after impact is calculated to be 6.71 m/s. The initial kinetic energy of the system is determined to be 111,600J, while the kinetic energy after the collision is calculated as 62,358J. To find the fraction of initial kinetic energy remaining, the ratio of final to initial kinetic energy is needed, clarifying that the question focuses on this fraction rather than the difference in energy values. The correct approach to the problem emphasizes understanding the ratio of kinetic energies rather than just calculating the energy difference.
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A 1550kg car, traveling with a velocity of 12m/s plows into a 1220kg stationary car. During the collision the two cars lock bumpers and then move together as a unit. (a) what is tehir common velocity just after the impact?
(b) What fraction of the initial kinetic energy remains after the collision.

(a) Pf=Pi

(m1+m2)vf=m1vi1
(1550kg+1220kg)vf=1550kg(12m/s)
2770kgvf=18600kg m/s

vf=6.71 m/s
I know my answer for part A is correct but part B i really have no idea how to approach it.
 
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rmarkatos said:
A 1550kg car, traveling with a velocity of 12m/s plows into a 1220kg stationary car. During the collision the two cars lock bumpers and then move together as a unit. (a) what is tehir common velocity just after the impact?
(b) What fraction of the initial kinetic energy remains after the collision.

(a) Pf=Pi

(m1+m2)vf=m1vi1
(1550kg+1220kg)vf=1550kg(12m/s)
2770kgvf=18600kg m/s

vf=6.71 m/s
I know my answer for part A is correct but part B i really have no idea how to approach it.
What is the initial kinetic energy of the system just before impact? What is the kinetic energy of the system immediately after impact? What is the ratio of the 2 values?
 
would the kinetic energy of the system just be the kinetic energy of the object the first car since the second one was stationary.

By the way the answer to the question is .559J from the odd selected answer section but i am not sure how to get the answer

ke=1/2mv^2
(1/2)(1550kg)(12m/s)^2
ke=111,600J

would the kinetic energy after be the sum of masses of the 2 cars with the shared final velocity?

ke=1/2mv^2
=(1/2)(2770kg)(6.71m/s)^2
=62358J the difference is not equal to .559J
 
rmarkatos said:
would the kinetic energy of the system just be the kinetic energy of the object the first car since the second one was stationary.

By the way the answer to the question is .559J from the odd selected answer section but i am not sure how to get the answer

ke=1/2mv^2
(1/2)(1550kg)(12m/s)^2
ke=111,600J

would the kinetic energy after be the sum of masses of the 2 cars with the shared final velocity?

ke=1/2mv^2
=(1/2)(2770kg)(6.71m/s)^2
=62358J the difference is not equal to .559J
Your calcs are correct, but they did not ask for the difference, they asked for the fraction of initial energy left. KE_f/KE_i = ??
 
ohhhhh your right thanks for clearing that up for me that makes a big difference
 

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