The diagram given below shows a ski jump. A skier weighing $60 \mathrm{kg}$ stands at $A$ at the top of the ski jump. He moves from $A$ to $B$ and takes off for his jump at $B$.

Calculate the change in the gravitational potential energy of the skier between $A$ and $B$. (Take $g=10 \mathrm{m}/{\mathrm{s}}^2$)
 

A hydroelectric power station takes its water from a lake whose water level is at a height of $50 \mathrm{m}$ above the turbine. Assuming an overall efficiency of $40\%$, calculate the mass of water which must flow through the turbine each second to produce power output of $1 \mathrm{MW}$. (Take $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)

The bob of a simple pendulum is imparted a velocity of $5 \mathrm{m}/\mathrm{s}$ when it is at its mean position. To what maximum vertical height will it rise on reaching at its extreme position if $60\%$ of its energy is lost in overcoming the friction of air? (Take $g=10 \mathrm{m}/{\mathrm{s}}^2$)