Solve for Initial Speed: Inelastic Collisions with Ballistic Pendulum

[patelkey]

Homework Statement

A bullet of mass 6 g strikes a ballistic pendulum of mass 2.0 kg. The center of mass of the pendulum rises a vertical distance of 14 cm. Assuming that the bullet remains embedded in the pendulum, calculate the bullet's initial speed.

Homework Equations

KE=1/2(mv^2)

3. The Attempt at a Solution [/b
The entire mass of pendulum & bullet rises 0.14 m,
this is a P.E. change of mgh (where m = 2.006 kg, h = 0.14 m)
P.E.(increase) = 2.006(9.81)(0.14) = 2.755 J
The initial K.E. of the bullet must equal this increase
1/2 mv² = 2.755
mv² = 5.510
v² = 5.510/0.006)
v² = 918.3
v = 30.3 m/s ANS

 

[ehild]

Conservation of energy is not valid for inelastic collision.

ehild