### NEET Solved Paper 2018 Question 30

##### Question: A body initially at rest and sliding along a frictionless track from a height h (as shown in the figure) just completes a vertical circle of diameter $ \text{AB=D} $ . The height h is equal to [NEET - 2018]

#### Options:

A) $ \frac{7}{5}D $

B) $ D $

C) $ \frac{3}{2}D $

D) $ \frac{5}{4}D $

## Show Answer

#### Answer:

Correct Answer: D

#### Solution:

As track is frictionless, so total mechanical energy will remain constant

$ T\text{.M}\text{.}{E_l}\text{=T}\text{.M}\text{.}{E_F} $

$ \text{0+mgh=}\frac{1}{2}mv _L^{2}+0 $ $ h=\frac{v_L^{2}}{2g} $

For completing the vertical circle,

$ v _{L}\ge \sqrt{5gR} $ $ h=\frac{5gR}{2g}=\frac{5}{2}R=\frac{5}{4}D $