$A$ pendulum of length $2\,m$ is released from point $P$ as shown in the figure. When it reaches point $Q$,it loses $10\%$ of its total energy due to air resistance. The velocity at $Q$ is .... $m/s$.

$A$ person of mass $60 \, kg$ wants to lose $5 \, kg$ by going up and down a $10 \, m$ high stairs. Assume he burns twice as much fat while going up than coming down. If $1 \, kg$ of fat is burnt on expending $7000 \, kcal$,how many times must he go up and down to reduce his weight by $5 \, kg$?

On complete combustion,a litre of petrol releases heat equivalent to $3 \times 10^7 \, J$. In a test drive,a car weighing $1200 \, kg$ (including the driver) travels $15 \, km$ per litre while moving at a uniform speed on a straight track. Assuming that the friction offered by the road surface and air is uniform,calculate the force of friction acting on the car during the test drive,given that the efficiency of the car engine is $0.5$. (in $, N$)

$A$ man throws a ball to a height of $12 \ m$,where it reaches with a speed of $12 \ m/s$. If the man throws the ball such that it just reaches this height,what percentage of energy would he have saved?

Two blocks $A(5 \ kg)$ and $B(2 \ kg)$ attached to the ends of a spring of spring constant $k = 1120 \ N/m$ are placed on a smooth horizontal plane with the spring undeformed. Simultaneously,velocities of $3 \ m/s$ and $10 \ m/s$ along the line of the spring in the same direction are imparted to $A$ and $B$. Then:

$A$ body of mass $1\,kg$ is thrown upwards with a velocity $20\,m/s$. It momentarily comes to rest after attaining a height of $18\,m$. How much energy is lost due to air friction? (Given $g = 10\,m/s^2$)