The mass of the kid and the sled is 50.0 kg
Explanation:
The sled starts to move when the force applied becomes larger than the maximum force of static friction, which is given by

where
is the coefficient of static friction
m is the mass of the kid + the sled
is the acceleration of gravity
Here the sled starts moving when the force applied is 61.2 N, so

And we also know

Therefore, we can find the mass of the kid and the sled by re-arranging the equation:

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The energy of a photon of light is directly proportional to its frequency and <span>inversely</span> proportional to its wavelength.
Friction is an example of thermal energy. As the tiny heat particles move, more warmness is made from the friction.