Question

A block of wood of mass 3 M is suspended by a string of length 10/3 m. A bullet of mass M hits is with a certain velocity and gets embedded it. The block and the bullet swing to one side till the string makes 120${}^0$ with the initial position. Find the velocity of the bullet $(g=10m{s}^{-2})$

• A. $\frac{40}{\sqrt{3}}m{s}^{-1}$
• B. $20m{s}^{-1}$
• C. $30m{s}^{-1}$
• D. $40m{s}^{-1}$

Answer 1

Answer: (D)

$40m{s}^{-1}$

Using energy conservation,
Potential energy change = Kinetic Energy
$1/2\left(4m\right)v^2=\left(4m\right)g\times (10/3+10/3sin{30}^{\circ })=20mg$
$v=10$
Using momentum conservation,
$mv=(m+3m)\left(10\right)\Rightarrow v=40m/s$.