Why does the recoiling nucleus have a smaller momentum than the alpha particle?

[jsmith613]

Homework Statement

A radium nucleus decays by emitting an alpha particle. The speed of the recoiling
nucleus is small compared to the speed of the alpha particle. This is because the:
A force acting on the recoiling nucleus is smaller than the force acting on the
alpha particle
B momentum is mainly concentrated in the alpha particle
C momentum of the recoiling nucleus is smaller than the momentum of the
alpha particle
D recoiling nucleus has a much larger mass than the alpha particle

why is it D?
http://www.edexcel.com/migrationdoc...E January 2010 - ER/6PH04_01_pef_20100310.pdf

Look at question 7)

for part (i) why is it C and

for part (iii) we were NOT told that O was stationairy so why is it D?

Homework Equations

The Attempt at a Solution

ok so for q3)
there is no way to conclude any of them
A: we don't know the accelerations
B: how much faster is it moving?
C: again we don;t know exact speeds
D: true but why relevant?

for Q7)
i) I would have said none of them can be KNOWN
but I would say X and Y have the same charge as they move in the same direction

ii) I got

iii)
we are not told if O is stationairy or not?

 

[jsmith613]

ok so I get the first one. momentum is conserved and the forces are the same due to netwon 3
but for Q7 in the paper I don't undertand i or iii)

 

[jsmith613]

sorry, wrong link see this one:
http://www.edexcel.com/migrationdoc...E January 2010 - QP/6PH04_01_que_20100128.pdf