$A$ small block of mass $m$ slides along a smooth track as shown in the figure. If it starts from rest at point $P$,what is the velocity of the block at point $Q$?

In the presence of which of the following is the work-energy theorem valid?

$A$ cricket ball of mass $0.15 \, kg$ is thrown vertically up by a bowling machine so that it rises to a maximum height of $20 \, m$ after leaving the machine. If the part pushing the ball applies a constant force $F$ on the ball and moves a distance of $0.2 \, m$ while launching the ball,the value of $F$ (in $N$) is $(g = 10 \, m/s^2)$.

$A$ bus moving on a level road with a velocity $v$ can be stopped at a distance of $x$ by the application of a retarding force $F$. The load on the bus is increased by $25\%$ by boarding the passengers. Now, if the bus is moving with the same speed and if the same retarding force is applied, the distance travelled by the bus before it stops is

$A$ pendulum bob has a speed of $3 \, m/s$ at its lowest position. The pendulum is $50 \, cm$ long. The speed of the bob, when the string makes an angle of $60^{\circ}$ to the vertical, will be $....... \, m/s$ $(g = 10 \, m/s^2)$.

Write the equation of total mechanical energy of a body of mass $m$ falling freely from a height $H$.