Question
Thu January 20, 2011 By: Azma Rahmani

A bullet with a velocity of 50m/s hits a block of wood and penetrates through a distance of 0.2 before coming to rest .the mass of the bullet is 0.03 kg . Calculate the resistance offered by the block of wood.

Expert Reply
Thu January 20, 2011
Dear student,
 
the resistance is the force which acted on the bullet and brought it to rest (or to a complete stop). A resistance is a force, however, it does not cause an object to move, but to slow it down or to stop it completely.

When an object is brought to rest, it means it has been stopped completely - no more movement. And that means that its final velocity is zero.

Mass of bullet 0.03kg ( initial velocity = 50ms-1, final velocity = 0, )

∆v = final velocity (zero) - initial velocity

final velocity = 0 because the bullet was brought to rest.

Therefore, ∆v = 50ms-1

Using the formula for force, F = m x ∆V/t   

F = 0.03 x 50/ 0.008

{D = v+u/2 *t

0.2 = 25 *t t = 0.008}

Hence, F = 187.5 N

Hope this helps.

Team

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