# HW11Sol - Jim Guinns PHYS2211 Assignment#11 Solutions These...

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Jim Guinn’s PHYS2211 Assignment #11 Solutions These problems are not to be turned in. They are for you to study for the exam. 1. A car has a mass of 1500kg. A truck has a mass of 19000kg and is moving at 30m/s . a.) At what speed would the car have the same magnitude of momentum as the truck? To have equal momenta we have m c v c = m t v t or v c = m t v t / m c = (19000kg) (30m/s) / (1500kg) = v c = 380m/s ! b.) At what speed would the car have the same kinetic energy as the truck. To have equal kinetic energies we have (1/2)m c v c 2 = (1/2)m t v t 2 or v c 2 = m t v t 2 / m c = (19000kg) (30m/s) 2 / (1500kg) = 11400m 2 /s 2 , so v c = 107m/s . Quite a bit less! 2. A 5.00kg mass is dropped (from rest) from 2.00m above the top of a large, vertically aligned spring. The spring has a spring constant of 100N/m . You must solve this using Conservation of Energy. (Hint: where do you want the gravitational potential energy equal to zero?) We set the gravitational and elastic potential energies at zero at the equilibrium point for the spring. Keep in mind that this will mean that when the mass compresses the spring, it will have a negative gravitational potential energy! The total initial energy is given by E i = (1/2)mv

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