A man jumps out of an airplane with a parachute. When he opens his parachute, he is plummeting to the ground at a rate of 100 mph. When he touches the ground 5 minutes later, he lands at a comfortable 10mph. What is his average acceleration during this time?

Question

Quizplus · Accepted Answer

Step 1: Find the acceleration
Acceleration = change in velocity ÷ time taken
The man starts at 100 mph and accelerates to 10 mph which makes the change in velocity:
10mph-100mph= -90mph
*Remember final velocity-initial velocity. So in this case, since the man starts out fast and slows down the acceleration is negative. 
The man took 5 minutes to reach the 10 mph velocity so the time taken equals 5 minutes.
Solve for a:
a = -90 mph / 5 minutes =  -18 mph/minute
Step 2: Convert units:
-18 mph/minute × 60 minutes = -1080 mph/hour

A Man Jumps Out of an Airplane with a Parachute