october november 2009 physics doubt

[angell]

Hey

so i had a doubt in Q.3

to calculate the kinetic energy they use 1.66

i just dont get why?

3 A stationary nucleus of mass 220u undergoes radioactive decay to produce a nucleus D of
mass 216u and an ?-particle of mass 4u, as illustrated in Fig. 3.1.

The initial kinetic energy of the ?-particle is 1.0 × 10–12 J.

(b) (i) Show that the initial speed of the ?-particle is 1.7 × 107 m s–1.


help, please?

[angell]

(b) (i) kinetic energy = ½ mv2
1.0 × 10-12 = ½ × 4 × 1.66 × 10-27 × v2
v = 1.7 × 107 m s-1


now WHY are they multiplying it 1.66?

[astarmathsandphysics]

mass of proton or neutron

[angell]

since when did the mass of a proton become 1.66

and we haven't done nuclear physics yet..maybe thats why.

[~Mimi~]

The rest mass of a proton is given on the first page of the exam.