•  A daring adventurer with a mass of 60 kg takes a bold leap from the edge of a cliff, which stands at a height of 50 meters. When he reaches the ground, he has a velocity of 20 m/s. Taking air resistance into account, solve the following:
• a. Determine the work done by friction during the descent (i.e., air resistance) 
• b. Find the magnitude of the frictional force acting on the adventurer. 
• c. Using the impulse-momentum theorem, calculate the net impulse experienced by the adventurer.  
• d. Calculate the total time the adventurer spends in the air during this leap.