Jonathan is riding a bicycle and encounters a hill of height 5.60 m. At the base
ID: 1447767 • Letter: J
Question
Jonathan is riding a bicycle and encounters a hill of height 5.60 m. At the base of the hill, he is traveling at 7.00 m/s. When he reaches the top of the hill, he is traveling at 2.00 m/s.Jonathan and his bicycle together have a mass of 77.0 kg. Ignore friction in the bicycle mechanism and between the bicycle tires and the road.
(a) What is the total external work done on the system of Jonathan and the bicycle between the time he starts up the hill and the time he reaches the top?
(b) What is the change in potential energy stored in Jonathan's body during this process?
(c) How much work does Jonathan do on the bicycle pedals within the Jonathan—bicycle—Earth system during this process?
Explanation / Answer
here,
height , h = 5.6 m
initial speed , u = 7 m/s
final speed , v = 2 m/s
mass , m = 77 kg
a)
the total external work done on the system of Jonathan and the bicycle , W = change in kinetic energy
W = 0.5 * m * ( v^2 - u^2)
W = 0.5 * 77 * ( 2^2 - 7^2)
W = - 693 J
b)
the change in potential energy stored in Jonathan's body during this process , PE = m * g * ( h - 0)
PE = 4225.76 J
c)
work done by Jonathan + work done by gravity = change in kinertic energy
W' = 4225.76 - 693
W' = 3532.8 J
work does Jonathan do on the bicycle pedals is 3532.8 J
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