You decide to try out your new rifle on a test range. The manufacturer says that

Question

You decide to try out your new rifle on a test range. The manufacturer says that a mb=4 g bullet is fired initially at a velocity of vb1=400 m/s . You decide to use this information to find the coefficient of friction between a block of wood and a concrete patio on which the block, mw=0.8 kg, rests. The bullet, when fired, passes entirely through the block and emerges from the other side at 120 m/s. The block of wood, initially at rest, slides 0.45 m before stopping. A) Find the speed of the block just after the bullet passes through. B) Find an expression for the coefficient of kinetic friction and compute its value C) How much kinetic energy does the bullet lose? D) What is the kinetic energy of the block just after the bullet exits the block?

Explanation / Answer

m1u1 = m1v1 + m2v2

v2 = (m1u1 - m1v1) = 1.12 m/s

now on 0.8 kg mass

v^2 = u^2 +2as

u^2 =2as

a = -1.39 m/s^2

Friction = ma

ukmg = ma

uk = a/g = 0.142

KE lost by bullet = 1/2 *m* (400^2 - 120^2) = 291.2 J

KE of block after passing = 1/2mv^2 = 0.5 J

a) vel of block =1.12 m/s

b)uk = 0.14

c)KE lost by bullet = 291.2 J

d)Ke of block = 0.5J

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