Question:

A bullet of mass 20g has an initial speed of 1ms⁻¹, just before it starts penetrating a mud wall of thickness 20cm. If the wall offers a mean resistance of 2.5×10⁻²N, the speed of the bullet after emerging from the other side of the wall is close to:

0.1ms⁻¹

0.7ms⁻¹

0.3ms⁻¹

0.4ms⁻¹

The correct option is D
0.7ms⁻¹
m=20g,u=1m/s,v=?
S=20×10⁻²m
a=-2.5×10⁻²/20×10⁻³m/s²
v²=u²+2as
v²=1-2×2.5×10⁻²/20×10⁻³×20×10⁻²
v=1-√2≈0.7m/s