# Homework Help: Binding energy question

1. Jan 29, 2006

### f4d_girl

"Calculate the total KE of the products of the reaction

13-C (d,n) 14-N if the incoming deuteron (d) has KE = 36.3 MeV"

I used the Q-value equation which is

Q = KEn + KEN - KEn - KEd

but to find the kinetic energy for each particle, velocity is required (which isn't given in the question)

So, i tried to use E=MC^2 and didn't work out well

to calculate the total KE of the products (KE of neutron and nitrogen)

can't i just use E=MC^2?

Thanks

Last edited: Jan 29, 2006
2. Jan 29, 2006

### Astronuc

Staff Emeritus
One has to use conservation of total energy, i.e the sum of kinetic and rest energies before = sum of kinetic and rest energies after.

The Q value is the difference in rest energy (masses). If Q > 0, the released energy is manifest in the kinetic energy of the products.

If Q < 0, some energy (e.g. kinetic energy of one or both reactants) must be applied.

3. Jan 29, 2006

### f4d_girl

umm okay
so you're saying that i should use KE before = KE after?
but the question is how do i find a kinetic energy of Carbon, neutron and nitrogen?
using E=mc^2?

4. Jan 29, 2006

### Astronuc

Staff Emeritus
Try KE (after) = KE (before) + Q or

KE(final) = KE(initial) + Q

and one can use classical mechanics for kinetic energy since 36.3 MeV << 1875.6 MeV (rest mass of d).

If one wants to calculate the specific kinetic energy of the particles, then one must apply conservation of momentum (a vector quantity) in both the x and y or longitudinal and transverse directions taken with respect to the incident velocity of the deuteron. A reasonable assumption would be that the beam of deuterons is impinging upon a fixed (solid) target of C.

Last edited: Jan 29, 2006
5. Jan 29, 2006

### f4d_girl

what i'm asking is, is KE(before) = 36.3 MeV?

KE= 0.5 mv^2, but velocity isn't given in the question

6. Jan 29, 2006

### f4d_girl

i still didn't get it
perhaps this is too complicated question for physics grade 12 IB
but thanks anyway

7. Jan 29, 2006

### Astronuc

Staff Emeritus
You are given the kinetic energy of 36.3 MeV, which is 1/2 mv2.

You could calculate v = sqrt(2KE/m).