Posted by **Scott** on Thursday, October 30, 2008 at 3:47pm.

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 è'2 = 45° from the neutron's initial direction. The neutron's initial speed is 6.6x10^5 m/s. Determine the angle at which the neutron rebounds, è'1, measured from its initial direction.

___°

What is the speed of the neutron after the collision?

___ m/s

What is the speed of the helium nucleus after the collision?

___ m/s

- General Physics -
**bobpursley**, Thursday, October 30, 2008 at 5:04pm
Elastic? Ok, momentum equations and energy equations can be used.

The sum of the final KE =initial KE

The sum of momentums in orig direction=momentum of neutron originally.

The sum of momentum in direction perpendicular to orig direction=zero

You will have three unknowns:

velocity of neutron after

velocity of He after

Theta.

Three equations, three unknowns. A little algebra and trig :)

- General Physics -
**Scott**, Thursday, October 30, 2008 at 5:38pm
thanks but I know that there are three unknowns and three equations. Getting the formulas are the difficult part.

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