Arturo O. answered • 12/17/15

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E1 = kinetic energy at v1 = 1000 J; v1 = 20 m/s; E2 = Kinetic energy at v2 = ?; v2 = 10 m/s; E1 = 1/2 m v1**2; E2 = 1/2 m v2**2; Use the given information to get m from E1 and V1, them plug the result into the expression for E2, using v2: m = 2 E1 / v1**2 = 2 (1000) / (20)**2 kg = 5 kg; Therefore, E2 = 1/2 m v2**2 = 1/2 (5) (10)**2 J = 250 J