8.68) A railroad handcar is moving along straight, frictionless tracks with negl

Question

8.68) A railroad handcar is moving along straight, frictionless tracks with negligible air resistance. In the following cases, the car initially has a total mass (car and contents) of 150 kg and is traveling east with a velocity of magnitude 5.20 m/s . Find the final velocity of the car in each case, assuming that the handcar does not leave the tracks.

A) An object with a mass of 25.0 kg is thrown sideways out of the car with a speed of 1.90 m/s relative to the car's initial velocity.

B) An object with a mass of 25.0 kg is thrown backward out of the car with a velocity of 5.20 m/s relative to the initial motion of the car.

C) An object with a mass of 25.0 kg is thrown into the car with a velocity of 6.10 m/s relative to the ground and opposite in direction to the initial velocity of the car.

Explanation / Answer

A) Using law of conservation of momentum

then momentum before thrown = momentum afte thrown

along east -west

150*5.2 = (150-25)*Vx

Vx = 6.24 m/sec

Along North -South

0 = (150-25)*Vy + (25*1.9)

Vy = -0.38 m/sec

then V = sqrt(vx^2+vy^2) = sqrt(6.24^2+0.38^2) = 6.25 m/sec

B) then momentum before thrown = momentum afte thrown

along east -west

150*5.2 = (150-25)*Vx -(25*5.2)

Vx = 7.28 m/sec

C) then momentum before thrown = momentum afte thrown

along east -west

150*5.2 = (150+25)*Vx -(25*6.1)

Vx = 5.32 m/sec

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