NEET UG 2020 — Mechanics

A ball is thrown vertically downward with a velocity of $20m{s}^{-1}$ from the top of a tower. It hits the ground after some time with a velocity of $80m{s}^{-1}$. The height of the tower is: $(g=10m{s}^{-2})$

A barometer is constructed using a liquid (density $=760\mathrm{kg}{m}^{-3}$) What would be the height of the liquid column, when a mercury barometer reads $76\mathrm{cm}?$ (density of mercury $=13600\mathrm{kg}{m}^{-3}$)

A body weighs $72N$ on the surface of the earth. What is the gravitational force on it, at a height equal to half the radius of the earth?

A capillary tube of radius $r$ is immersed in water and water rises in it to a height $h$. The mass of the water in the capillary is $5g$. Another capillary tube of radius $2r$ is immersed in water. The mass of water that will rise in this tube is:

A liquid does not wet the solid surface if angle of contact is:

A person sitting in the ground floor of a building notices through the window, of height $1.5m,$ a ball dropped from the roof of the building crosses the window in $0.1s.$ What is the velocity of the ball when it is at the topmost point of the window? $(g=10m{s}^{-2})$

A plano-convex lens of unknown material and unknown focal length is given. With the help of a spherometer we can measure the

A point mass $m$ is moved in a vertical circle of the radius $r$ with the help of a string. The velocity of the mass is $\sqrt{7gr}$ at the lowest point. The tension in the string at the lowest point is:

A screw gauge has least count of $0.01\mathrm{mm}$ and there are $50$ divisions in its circular scale. The pitch of the screw gauge is:

A wire of length $L$, area of cross section $A$ is hanging from a fixed support. The length of the wire changes to ${L}_{1}$ when mass $M$ is suspended from its free end. The expression for Young's modulus is:

Calculate the acceleration of the block and trolly system shown in the figure. The coefficient of kinetic friction between the trolly and the surface is $0.05.$ ($g=10m{s}^{-2},$ mass of the string is negligible and no other friction exists). 

Dimensions of stress are:

Find the torque about the origin when a force of $3\hat{j}N$ acts on a particle whose position vector is $2\hat{k}m$.

Taking into account of the significant figures, what is the value of $9.99m–0.0099m$?

The angle of $1'$ (minute of arc) in radian is nearly equal to

The angular speed of the wheel of a vehicle is increased from, $360\mathrm{rpm}$ to $1200\mathrm{rpm}$ in $14s$. Its angular acceleration is,

The energy required to break one bond in DNA is ${10}^{–20}J$. This value in $\mathrm{eV}$ is nearly

Three identical spheres, each of mass $M,$ are placed at the corners of a right angle triangle with mutually perpendicular sides equal to $2m$ (see figure). Taking the point of intersection of the two mutually perpendicular sides as the origin, find the position vector of centre of mass. 

Time intervals measured by a clock give the following readings: $1.25s,1.24s,1.27s,1.21s$ and $1.28s$. What is the percentage relative error of the observations?

Two bodies of mass $4 \mathrm{kg}$ and $6 \mathrm{kg}$ are tied to the ends of a massless string. The string passes over a pulley which is frictionless (see figure). The acceleration of the system in terms of acceleration due to gravity $(g)$ is: 

Two particles of mass $5 \mathrm{kg}$ and $10 \mathrm{kg}$ respectively are attached to the two ends of a rigid rod of length $1 m$ with negligible mass. The centre of mass of the system from the $5 \mathrm{kg}$ particle is nearly at a distance of:

What is the depth at which the value of acceleration due to gravity becomes $\frac{1}{n}$, times the value at the surface of the earth? (radius of the earth $=R$)