A block of wood has mass m=0.266kg and cross-sectional dimensions viewed side on a=0.06m and b=0.12m.
Two tests are carried out firing bullets into the block of wood. In both cases a bullet of mass m=98g and velocity v=287m/s is fired vertically upward from below the block.
Case A: The bullet is made to have a direct central impact with the block. i.e. . Case B: The bullet is fired to one side of the mass centre of the wood. i.e. mm.

In case A, what percentage of the bullet’s initial kinetic energy is conserved as kinetic energy in the impact?

Question

A block of wood has mass m=0.266kg and cross-sectional dimensions viewed side on a=0.06m and  b=0.12m.
Two tests are carried out firing bullets into the block of wood. In both cases a bullet of mass m=98g and velocity v=287m/s is fired vertically upward from below the block.
Case A: The bullet is made to have a direct central impact with the block. i.e.  . Case B: The bullet is fired to one side of the mass centre of the wood. i.e.  mm.

In case A, what percentage of the bullet’s initial kinetic energy is conserved as kinetic energy in the impact?

anonymous · Answer

"Hint: You may assume that the centre of mass of the system of bullet and block is the geometric centre of the block of wood and the bullet penetrates to exactly half of the block’s thickness."

|dw:1383631377079:dw|

Not sure where to start, when calculating Kinetic energy after.