hi, i need help please, i have 2 questions i need their completesolutions 1) A m

Question

hi,
i need help please, i have 2 questions i need their completesolutions

1)
A machine gun is attached to a railroad flatcar that rolls withnegligible friction. If the railroad car has a mass of 6.25 ´104 kg, how many bullets of mass 25 g would have to be fired at 250m/s off the back to give the railroad car a forward velocity of 0.5m/s?

2)
A 2 500-kg truck moving at 10.00 m/s strikes a car waiting at atraffic light, hooking bumpers. The two continue to move togetherat 7.00 m/s. What was the mass of the struck car?

thanks in advance..

Explanation / Answer

According to the law of conservation of momentum,we have M * u + m * u1 = (M + m) * V or M * u = (M + m) * V or m = M * (u/v - 1) or m = 2500 * (10.00/7.00 - 1) or m = 1071 kg Therefore,the mass of the struck car is m = 1071 kg.

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