1. How much work is required to stop an electron, m = 9.31x10-31 kg, which is moving with a speed of 1.90x106 m/s?
2. A weighlifter raises a 180-kg barbell to a height of 1.95 m. What is the increase in the barbell's potential energy?
3. A rifle can fire a 4.20-gram bullet at a speed of 965 m/s.
(a) How much work is done on the bullet?
(b) If the length of the barrel is 75 cm, how much force accelerates the bullet?