A boy riding a bicycle begins from rest and moves down a hill that is inclined at $30^\circ$ to the horizontal. The boy together with the bicycle has a total mass of $25\,\text{kg}$. A frictional force of $30\,\text{N}$ acts, and this force does not depend on the bicycle’s velocity. What is the kinetic energy of the boy and the bicycle after they have travelled $20\,\text{m}$ down the slope?
- A$1850\,\text{J}$
- B$2450\,\text{J}$
- C$3050\,\text{J}$
- D$3640\,\text{J}$