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Homework Help: Determine the angle of the neutron

  1. Nov 2, 2008 #1
    A neutron collides elastically with a helium nucleus (at rest initially) whose mass is four times that of the neutron. The helium nucleus is observed to move off at an angle θ'2 = 45° from the neutron's initial direction. The neutron's initial speed is 7.0 × 105 m/s.

    a) Determine the angle of the neutron, θ'1, measured from its initial direction.

    b) What is the speed of the neutron, vn', after the collision?

    c) What is the speed of the helium nucleus, vHe', after the collision?

    x direction: m1*7.0x10^5+0=m1*v1'*Cosθn+4*m1*v2'*Cos45

    y direction: 0=-m1*v1'*Sinθn+4*m1*v2'*Sin45

    Change in KE: 1/2*m1*(7.0x10^5)^2=1/2*m1*v1'^2+1/2*4*m1*v2'^2

    I know mass cancels and I need to do algebra to figure out the answer, but I am having trouble doing the algebra with so many unknowns.
    Can anyone lend me a helping hand?
    Last edited: Nov 2, 2008
  2. jcsd
  3. Nov 3, 2008 #2
    I figured it out ;)
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