Transcript Conservation of Momentum

Conservation of Momentum
Sample Problems
Conservation of Momentum
Problem 1
Glider A of mass 0.355 kg moves along a frictionless air track
with a velocity of 0.095 m/s. It collides with glider B of mass
0.710 kg moving in the same direction at a speed of 0.045
m/s. After the collision, glider A continues in the same
v m v m v 
  m velocity
direction with a velocity of 0.035 m/s. What isv the
of
m
glider B after the collision?
A A
B B
A A
B
B
KNOWN:
mA = 0.355 kg
vA = 0.095 m/s
mB = 0.710 kg
vB = 0.045 m/s
vA ‘ = 0.035 m/s
UNKNOWN:
vB ‘ = ?
REMEMBER: mAvA + mBvB = mAvA‘ + mBvB'

m
v

m
v

m
v
A
A
B
B
A
A
vB 
mB
(0.355kg)(0.095m / s)  (0.710kg)(0.045m / s)  (0.355kg)(0.035m / s)

vB 
0.710kg
vB‘ = 0.075 m/s
Conservation of Momentum
Problem 2
A 20 g bullet strikes an 8 kg stationary wooden block and
embeds itself in the block. The block and the bullet fly off
together at 10 m/s. What was the original velocity of the bullet?
REMEMBER: mBvB + mWvW = (mB + mW)v'
KNOWN:
mB = 0.020 kg
mw = 8 kg
Since vW = 0, we can eliminate this quantity.
mB vB  (mB  mW )v 
vW = 0 m/s
v' = 10 m/s
UNKNOWN:
vB = ?
vB 
( mB  mW ) v
mB
(0.020kg  8kg )10m / s
vB 
0.020kg
vB = 4 x 103 m/s