•A ballistic pendulum is a device in which a projectile is fired into a pendulum, and after firing, the projectile and the pendulum swing together to some final height h.

h

• The speed of the projectile can be determined by using:

h

1) The conservation of momentum principle during the collision of the projectile with the pendulum

2) The conservation of energy principle after the collision,

Example A 10.0 g bullet is fired into a 4.00 kg block which then swings to a height of 0.205 m. Determine the speed of the bullet before the collision.

Use energy conservation after the collision:

topEbottom

E

Ep bot + Ek bot = Ep top + Ek top mghbot + ½ mv2

bot = mghtop + ½ mv2top

0 J + ½ mv2bot = mghtop + O J

½ mv2 = mgh m = mbullet+mblock

)205.0)(/81.9(2

2

2 msmv

ghv

v = 2.0055 m/s (speed of block and bullet after the collision)

Use conservation of momentum for the collision:

kg

smkgv

vmp

smkgp

smkgkgp

ppp

pp

bullet

bulletbulletbullet

bullet

bullet

blockbulletblockbullet

afterbefore

3

3

100.10

/04212.8

/04212.8

)/0055.2)(100.1000.4(0

'

vbullet = 804 m/s

A ballistic pendulum experiment:

(metal rod versus watermelon)

A ballistic pendulum experiment:

(metal rod versus watermelon)

(Out-take)