REMARKS Because the impact is inelastic, it would be incorrect to equate the ini

Question

REMARKS Because the impact is inelastic, it would be incorrect to equate the initial kinetic energy of the incoming bullet to the final gravitational potential energy associated with the bullet–block combination. The energy isn't conserved!

QUESTION The ways that mechanical energy is lost from the system in this experiment include: (Select all that apply.)

emission of sound wavesfriction in the mechanismsenergy loss from the change in height of the blockfriction to bring the bullet to a stop relative to the groundthermal energy loss due to air drag

PRACTICE IT

Use the worked example above to help you solve this problem. The ballistic pendulum (Figure a) is a device used to measure the speed of a fast-moving projectile such as a bullet. The bullet is fired into a large block of wood suspended from some light wires. The bullet is stopped by the block, and the entire system swings up to a height h. It is possible to obtain the initial speed of the bullet by measuring h and the two masses. As an example of the technique, assume that the mass of the bullet, m1, is 5.31 g, the mass of the pendulum, m2, is 1.074 kg, and h is 5.23 cm.

(a) Find the velocity of the system after the bullet embeds in the block.
m/s

(b) Calculate the initial speed of the bullet.
m/s

EXERCISEHINTS:  GETTING STARTED  |  I'M STUCK!

(a) Find the initial speed of the bullet–block system.
m/s

(b) Find the speed of the bullet.
m/s

Explanation / Answer

PRACTICE iT:

(A) Applying energy cosneravation,

PEi + KEi = PEf + KEf

0 + m v^2 /2 = m g h + 0

v = sqrt(2 x 9.8x 0.0523) = 1.012 m/s

(B) Applying momentum conservation for the collision,

(0.00531 v0) + (1.0174 x 0) = (1.074 + 0.00531) (1.012)

v0 =205.8 m/s

EXERCISE:

(A) Applying energy conservation,

k x^2 / 2 = m v^2 /2

(614)(0.0563^2) = (1.977 + 0.00488) v^2

v = 0.99 m/s

(B) Applying momentum cosnervation,

(0.00488)v0 = (1.977 + 0.00488)(4.18)

v0 = 402.4 m/s

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