A puck of mass m 1 = 0.43 kg and speed 3.0 m/s collides with a 0.9 kg moving in

Question

A puck of mass m1 = 0.43 kg and speed 3.0 m/s collides with a 0.9 kg moving in the same direction at 0.7 m/s.

a) What is in Kg m/s the overall momentum of the pucks before the collision?

b) What is in Joules the overall kinetic energy of the pucks before the collision?

After the collision, m1 bounces back with a speed of 0.1 m/s.

c)  What is in m/s the speed of the second puck after the collision?

d) What is in Joules the overall kinetic energy of the pucks after the collision?

e) Which of these is statements is the correct statement:
the collision is elastic because momentum is conserved
the collision is elastic because both momentum and kinetic energy are conserved
the collision is elastic because momentum is conserved and m1 bounced back
the collision is elastic because kinetic energy is conserved and m1 bounced back
  the collision is elastic because the masses did not attach
the collision is elastic because the masses did not attach and the momentum is conserved

Explanation / Answer

The total momentum of the two pucks is zero before the collision and after the collision.
Let particle 1 be the green puck and particle 2 be the blue puck. Before and after the collision the ratio of the speeds is v2/v1 = m1/m2 = 1/1.2.
The final kinetic energy of the system equals 1/2 time its initial kinetic energy.
(1/2)m1v1i2 + (1/2)m2v2i2 = 2((1/2)m1v1f2 + (1/2)m2v2f2).
m1v1i2 + m2v2i2 = 2(m1v1f2 + m2v2f2).
m1v1i2 + 1.2m1(v1i/1.2)2 = 2(m1v1f2 + 1.2m1(v1f/1.2)2).
m1(v1i2 + v1i2/1.2) = 2m1(v1f2 + v1f2/1.2).
v1i2 = 2v1f2, v1f = 0.707v1i.
v1f = 7.07 m/s. v2f = 5.89 m/s.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.