# physics

a bullet of mass 20g is fired into a block of wood of mass 400g . if the bullut and wood move together with speed of 20ms-1 calclate(i) speed with the bullet hits the wood ii the kinetic energy lost iii state the energy changes involed

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1. bullet momentum = m v = .020 v

final momentum = (.020 + .400)(20)
so
v of bullet = (.020 + .400)(20) / (.020)

initial Ke = (1/2) (.020) v^2

final Ke = (1/2)(.420)(400) It better be less :)

so loss to heat = final Ke - initial Ke

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