Two hockey pucks are on a collision course with one and another. Puck 1 has a ma

Question

Two hockey pucks are on a collision course with one and another. Puck 1 has a mass of 0.22 kg and a speed of 1.3 m/s. Puck 2 has a mass of 0.38 kg. a. What speed must puck 2 have in order for the total momentum to be zero? b. If the momentum of the system is zero, does it make sense for the kinetic energy to also be zero? Verify your answer by doing the calculations. An 88 kg astronaut is floating by a 1500 kg satellite, and they are both at rest relative to the space shuttle. The astronaut pushes on the satellite giving it a speed of 0.14 m/s directly away from the shuttle. If the astronaut comes into contact with the shuttle 9.3 s later, how far was the astronaut from the shuttle initially? A cart of mass m and speed v moves on a frictionless track and collides with an identical cart. If the two carts stick together after the collision, what is the final kinetic energy of the system? An 829 kg car idling behind a red light is rear-ended by a 1650 kg truck moving with a speed of 16.5 m/s. If the car was in neutral and its brakes off, so that the collision is elastic, find the speed of both vehicles after the collision.

Explanation / Answer

here,

1)

mass of puck 1 , m1 = 0.22 kg

mass of puck 2 , m2 = 0.38 kg

initial speed of 1 , u1 = 1.3 m/s

let the initial speed of 2 be u2 for total momentum be zero

m1 * u1 + m2 * u2 = 0

0.22 * 1.3 + 0.38 * u2 = 0

u2 = - 0.75 m/s

the initial speed of 2 is - 0.75 m/s

b)

No, it does not make any sense

when the momentum is zero, the total kinetic energy may or may not be zero

for this question

the total momentum is zero

but the total kinetic energy , KE = 0.5 * m1 * u1^2 + 0.5 * m2 * u2^2

KE= 0.5 * 0.22 * 1.3^2 + 0.5 * 0.38 * ( -0.75)^2

KE = 0.29 J

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