Correct Answer is B according to my professor but I don\'t understand why? A sle
ID: 1628772 • Letter: C
Question
Correct Answer is B according to my professor but I don't understand why?
A sled of mass m is coasting at a constant velocity on the ice covered surface of a lake. Three birds, with a combined mass 0.5m, gently land at the same time on the sled. The sled and birds continue sliding along the original direction of motion. How does the kinetic energy of the sled and birds compare with the initial kinetic energy of the sled before the birds landed?
a) The final kinetic energy is one half of the initial kinetic energy.
b) The final kinetic energy is one third of the initial kinetic energy.
c) The final kinetic energy is one quarter of the initial kinetic energy.
d) The final kinetic energy is one ninth of the initial kinetic energy.
e) The final kinetic energy is equal to the initial kinetic energy.
Explanation / Answer
Conserving momentum
mv = 1.5mv'
v' = 2/3v
KE_i = 0.5mv^2
KE_f = 0.5*1.5m*(2/3v)^2 = (1/3)KE_i
Hence answer is B