[snowboard125]

Please Help! Been trying to solve this for an hour!
A 1.6 kg colt automatic pistol fires a 15 g bullet into a 2.5 kg wooden block suspended from the ceiling as a ballistic pendulum. The bullet becomes imbedded in the block 6.9 x 10^–4 s after first contact. The bullet and block swing east and rise to a height of 9.8 cm above the rest position. Based on the information in the above narrative, the velocity of the bullet was?

I put x for Vinitial at first, Found Vf by applying the Ek=Ep formula which was, 1/2(mb+mbl)v^2 = 1/2(mb+mbl)gh, then used the Sysi1+Sysi2=Sysf1+Sysf2, to find the initial velocity of the bullet, but all of these were wrong! Do I have to do something with the mass of a pistol and the time it took for the bullet to hit the block? If so, I don't have the force, to do a=F/m equation. Please help me :(

[ebaines]

Your approach should give the initial velocity of the bullet and block as it starts its upward swing, although the expression for potential energy is mgh not 1/2 mgh. Then you can use conservation of momentum: m1v1=(m1+m2)v2 to find the velocity of the bullet.