(a) How many joules of kinetic energy does a 65-kg person have when walking at 2
ID: 1332485 • Letter: #
Question
(a) How many joules of kinetic energy does a 65-kg person have when walking at 2 m/s?
J
How many joules of kinetic energy does a 65-kg person have when running at 6 m/s?
J
(b) In the Bohr model of the atom, the ground-state electron in hydrogen has an orbital speed of 2190 km/s. What is its kinetic energy?
J
(c) If you drop a 8.0 kg weight (about 18 lb) from shoulder height (1.6 m), how many joules of kinetic energy will it have when it reaches the ground?
J
(d) Is it reasonable that a 40-kg child could run fast enough to have 85 J of kinetic energy?
Yes or No
Explanation / Answer
(a) kinetic energy = 0.5 m v^2 = 0.5 * 65 * 2^2 = 130 J
kinetic energy = 0.5 m v^2 = 0.5 * 65 * 6^2 = 1170 J
(c) Conservation of energy
KE = PE = m g h = 8 * 9.81 * 1.6 = 125.57 J
(d) KE = 0.5 m v^2
v = sqrt( 2 KE / m) = sqrt(2*85/40) = 2.06 m/s
Yes. it is reasonable
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