A machine gun is attached to a railroad flatcar that rolls with negligible 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 250 m/s off the back to give the railroad car a forward velocity of 0.3 m/s?
a. 400
c. 3000
b. 2000
d. 5000
Question 2
A proton (+1.6 10-19 C) moves 10 cm on a path in the direction opposite to a uniform electric field of strength 3.0 N/C. How much work is done on the proton by the electrical field?
a. 4.8 10-20 J
c. zero
b. 1.6 10-20 J
d. -4.8 10-20 J
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