Question

A small block of mass $M$ moves on a frictionless surface of an inclined plane, as shown in the figure. The angle of the incline suddenly changes from $60^?$ to $30^?$ at point $B$. The block is initially at rest at $A$. Assume that collisions between the block and the incline are totally inelastic, the speed of the block at point $C$, immediately before it leaves the second incline is

• A. $\sqrt{120}\,m/s$
• B. $\sqrt{105}\,m/s$
• C. $\sqrt{90}\,m/s$
• D. $\sqrt{75}\,m/s$

Answer 1

Answer: (B)

$\sqrt{105}\,m/s$

Answer 2

Mechanical energy conservation between points $B$ and $C$ gives $v^{2}_{C} = v^{2}_{B}+2\,gh$ or $v^{2}_{C} = 45+2\times10 \times 3$ $\Rightarrow v_{C} = \sqrt{105}\,m/s$.