Question

You Fire A Bullet Into A 3 Kg Wooden Block Attached To A Spring With Spring Constant 70 N/m. When The Bullet Strikes The Block, The Spring Compresses. The Bullet Has A Mass Of 0.03 Kg And Strikes The Block With A Speed Of 200 M/s. What Is The Speed Of The Block And Bullet When They First Start Moving Together?

Answer 1

here at the moment when bullet strikes the block it will have no external force on it

so here we can use momentum conservation

so we will have

$P_i = P_f$

$m_1v_{1i} + m_2v_{2i} = m_1v_{1f} + m_2v_{2f}$

$0.03(200) + 3(0) = 0.03v + 3v$

$6 = 3.03v$

$v = \frac{6}{3.03}$

$v = 1.98 m/s$

so they move together with speed 1.98 m/s