Answer:
Explanation: simple kinematics
we suppose that initially vo= 0 so if the skier moves 4s :
vf = vo +at = 0 + 3*4 = 12 m/s
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ANSWER:
3408.81 kg
STEP-BY-STEP EXPLANATION:
Given:
v = 111 m/s
Ek = 21000000 J
We have that the formula for kinetic energy is as follows:

We substitute the values given in the exercise and solve for m (mass)

The mass of the helicopter is 3408.81 kilograms.