Problem 4. Snowboarder Gavrila descended a hill 250 meters high and had a speed of 10 m/s at the foot of the hill. What fraction of the total loss of mechanical energy during the descent went to heating the snowboard weighing 6 kg, if it heated up by 1 degree? The specific heat capacity of the snowboard material is 300 J/kg $\cdot$ K. Gavrila's weight with full equipment is 72 kg.
Solution. The law of change of mechanical energy during descent $\frac{m V^{2}}{2}=m g H-W$. From this, the energy loss $W=m g H-\frac{m V^{2}}{2}=72 \cdot 10 \cdot 250-36 \cdot 100=36 \cdot 4900$ J.

The amount of heat $Q=c \cdot m \cdot\left(T-T_{0}\right)=300 \cdot 6 \cdot 1=1800$.

The required value $k=\frac{Q}{W}=\frac{6 \cdot 300}{36 \cdot 4900}=\frac{1}{98}$.

Answer: $1 / 98$.