A bullet with mass of 0,005g hits a wooden block with a mass of 1,2kg velocity

[pirates]

Homework Statement

A bullet with mass of 0,005g hits a wooden block with a mass of 1,2kg. The bullet and the block move 0,3meters after the collision, friction coefficient is 0,2 between the ground and the block. Find out velocity of the bullet.

Trying to study for exams, but got stuck in this question

The Attempt at a Solution

V1 = ?
V2 = ?
m1 = 0,005kg
m2= 1,2kg
l = 0,3m
u= 0,2

we know that kinetic energy of the bullet is 1/2mv^2, after the bullet hits the block, the kinetic energy is converted into friction work, that is needed to move the block

so 1/2mv^2 = Fu * 0,3m
v^2 = ( 2 ( 0,005kg+1,2kg) * 9,8m/s^2 * 0,2 * 0,23m) / 0,005kg
and v= squareroot ( ...)

what am I doing wrong?

 

[tiny-tim]

Hi pirates!

A bullet with mass of 0,005g hits a wooden block with a mass of 1,2kg. The bullet and the block move 0,3meters after the collision, friction coefficient is 0,2 between the ground and the block. Find out velocity of the bullet.
…
we know that kinetic energy of the bullet is 1/2mv^2, after the bullet hits the block, the kinetic energy is converted into friction work, that is needed to move the block …

No, this is an inelastic collision … energy is not conserved at the start …

for the start, you have to use conservation of momentum