A 15.0-g bullet is fired into a 1,500-g block of wood which is suspended as a ballistic pendulum.The combined mass swings up to a height of 8.50 cm.What was the kinetic energy of the combined mass immediately after the collision?

Question

Quizplus · Accepted Answer

To solve this problem, we can use the conservation of momentum and conservation of energy equations. First, we can use conservation of momentum to find the velocity of the combined mass immediately after the collision:
m_bullet * v_bullet = (m_bullet + m_block) * v_combined
15g * v_bullet = (15g + 1500g) * v_combined
v_combined = 15g * v_bullet / 1515g

Next, we can use conservation of energy to find the kinetic energy of the combined mass at this velocity:
KE_combined = (1/2) * (m_bullet + m_block) * v_combined^2
KE_combined = (1/2) * 1515g * ((15g * v_bullet / 1515g)^2)
KE_combined = 1.262 J (to three significant figures)

A 150-G Bullet Is Fired into a 1,500-G Block of Wood