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JEE Advance - Physics (2008 - Paper 1 Offline - No. 21)

A small block of mass M moves on a frictionless surface of an inclined plane, as shown in figure. The angle of the incline suddenly changes from 60$$^\circ$$ to 30$$^\circ$$ at point B. The block is initially at rest at A. Assume that collisions between the block and the incline are totally inelastic (g = 10 m/s$$^2$$).

A small block of mass M moves on a frictionless surface of an inclined plane, as shown in figure. The angle of the incline suddenly changes from 60$$^\circ$$ to 30$$^\circ$$ at point B. The block is initially at rest at A. Assume that collisions between the block and the incline are totally inelastic (g = 10 m/s$$^2$$).

A small block of mass M moves on a frictionless surface of an inclined plane, as shown in figure. The angle of the incline suddenly changes from 60$$^\circ$$ to 30$$^\circ$$ at point B. The block is initially at rest at A. Assume that collisions between the block and the incline are totally inelastic (g = 10 m/s$$^2$$).

The speed of the block at point B immediately after it strikes the second incline is
$$\sqrt{60}$$ m/s
$$\sqrt{45}$$ m/s
$$\sqrt{30}$$ m/s
$$\sqrt{75}$$ m/s

Explanation

Velocity along the plane just before collision,

$${v^2} - {u^2} = 2gs \Rightarrow v = \sqrt {2g \times 3} = \sqrt {60} \,m/s$$

Velocity along the plane just after collision

$${v_B} - v\cos 30 = \sqrt {45} \,m{s^{ - 1}}$$

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