A neutron of mass m moving with velocity v collides head-on and elastically with a stationary nucleus of mass M. (a) Show that the velocity of the nucleus after the collision, U, is given by ( ) v m M m U + = 2 (b) Hence show that the neutron loses a fraction f of its energy where ( ) 2 4 m M mM f + = (c) A fast neutron enters a target of carbon nuclei which may be assumed to have masses 12 times that of the neutron. How many head-on collisions will it take before the neutron loses 95% of its energy? (d) Suggest one reason why in a real reactor a neutron is likely to make more collisions with the moderator nuclei before losing this much energy​

Multiple choice. choose the one alternative that best completes the statement or answers the question. 1) if the force on an object is in the negative direction, the work it does on the object must be 1) a) negative. b) positive. c) the work could be either positive or negative, depending on the direction the object moves. 2) a truck has four times the mass of a car and is moving with twice the speed of the car. if kt and kc refer to the kinetic energies of truck and car respectively, it is correct to say that 2) a) kt = 16kc . b) kt = 1 2 kc. c) kt = kc . d) kt = 2kc . e) kt = 4kc . 3) you and your friend, who weighs the same as you, want to go to the top of the eiffel tower. your friend takes the elevator straight up. you decide to walk up the spiral stairway, taking longer to do so. compare the gravitational