Car A hits car B (initially at rest and of equal mass) frombehind while going 35 m/s. Immediately after the collision, car Bmoves forward at 25 m/s and car A is at rest. What fraction of theinitial kinetic energy is lost in the collision?
My approach:
How exactly do you approach this question? At first, I thoughtusing the the formula ΣKEi = ΣKEf.Then, to find the fraction just divide the former from the latter.But is it that cut and dry?
Before collision:
viA= 35 m/s
viB = 0 m/s
vfA = 0 m/s
vfB =25 m/s
m1 = m2

Respuesta :

Answer:

The fraction of kinetic energy lost in the collision in term of the initial energy is 0.49.

Explanation:

As the final and initial velocities are known it is possible then the kinetic energy is possible to calculate for each instant.

By definition, the kinetic energy is:

k = 0.5*mV^2

Expressing the initial and final kinetic energy for cars A and B:

[tex]ki=0.5*maVa_{i}^2+0.5*mbVb_{i}^2[/tex]

[tex]kf=0.5*maVa_{f}^2+0.5*mbVb_{f}^2[/tex]

Since the masses are equals:

[tex]m=ma=mb[/tex]

For the known velocities, the kinetics energies result:

[tex]ki=0.5*mVa_{i}^2[/tex]

[tex]ki=0.5*m(35 m/s)^2=612.5m^2/s^2*m[/tex]

[tex]kf=0.5*mbVb_{f}^2[/tex]

[tex]kf=0.5*m(25 m/s)^2=312.5m^2/s^2*m[/tex]

The lost energy in the collision is the difference between the initial and final kinectic energies:

[tex]kl=ki-kf[/tex]

[tex]kl = 612.5m^2/s^2*m-312.5 m^2/s^2*m=300 m^2/s^2*m [/tex]

Finally the relation between the lost and the initial kinetic energy:

[tex] kl/ki = 300 m^2/s^2 * m / 612.5 m^2/s^2 * m [/tex]

[tex]kl/ki = 24/49=0.49 [/tex]

Based on the data provided, the fraction of the initial kinetic energy is lost in the collision is 48.9%.

What is the momentum?

Momentum isbthe product of mass and velocity of a body.

  • Momentum = mass × velocity

From the principle of conservation of momentum, the momentum is conserved in an isolated system of colliding bodies.

Momentum before collision = Momentum after collision.

Kinetic energy = 1/2mv^2

Since the mass are the same, difference in kinetic energy s due to change in velocity.

Change in velocity = 25 - 35 = -10 m/s

Kinetic energy before collision = 1/2× 35 × 35 × m = 612.5m J

Kinetic energy after collision = 1/2 × 25 × 25 × m = 312.5 m J

Loss in Kinetic energy = 612.5m - 312.5m = 300m J

Fraction lost = 300m / 612.5 × 100 = 48.9%

Therefore, the fraction of the initial kinetic energy is lost in the collision is 48.9%.

Learn more about momentum and kinetic energy at: https://brainly.com/question/1468572