In: Physics
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 rebound at an angle x = 43° from the neutron's initial direction. The neutron's initial speed is 6.4*10^5 m/s. Determine the angle at which the neutron rebounds, measured from its initial direction.
a) Incorrect: Your answer is incorrect. 73.96°
b) What is the speed of the neutron after the collision? Incorrect: Your answer is incorrect. 187226.4m/s
c) What is the speed of the helium nucleus after the collision? Incorrect: Your answer is incorrect. 545854.07 m/s
The x and y axis are chosen as shown in the diagram. The positive x axis is along the direction of v2 (final velocity of He nucleus). The y axis is the axis perpendicular to it.
The components of momentum along these x and y axis are calculated.
Conservation of momentum equations are set up for these components as follows:
Horizontal direction:
Total initial momentum along x axis = total final momentum along x axis.
So, mXu1XCos43 = 4XmXv2 + mXv1x
where u1 = 6.4X105 m/s
So, v1x = 468066.3690 - 4 X v2 ------ |
(1) |
Total initial momentum along y axis = total final momentum along y axis.
So, mXu1XSin47 = mXv1y
So, v1y = 468066.3690 m/s ------- |
(2) |
By conservation of kinetic energy in elastic collisions,
total initial kinetic energy = total final kinetic energy.
-------------(3)
---------------(4)
By using all above four equations, we get
v2 = 187226.4 m/s
substitute v2 in eq (5) then we get
v1x = -280839.231 m/s
v1 = -280839.231 i + 468066.3690 j
= 468066.3690 /280839.231
= 59.030
angle at which neutron rebounds, measured from its initial direction, θ1 = 430 + 900 - = 73.970
magnitude of v1 = 545854.1925 m/s