Answer:
v = 12.52 [m/s]
Explanation:
To solve this problem we must use the energy conservation theorem. Which tells us that potential energy is transformed into kinetic energy or vice versa. This is more clearly as the potential energy decreases the kinetic energy increases.
Ep = Ek
where:
Ep = potential energy [J] (units of joules]
Ek = kinetic energy [J]
Ep = m*g*h
where:
m = mass of the rock = 45 [g] = 0.045 [kg]
g = gravity acceleration = 9.81 [m/s²]
h = elevation = (20 - 12) = 8 [m]
Ek = 0.5*m*v²
where:
v = velocity [m/s]
The reference level of potential energy is taken as the ground level, at this level the potential energy is zero, i.e. all potential energy has been transformed into kinetic energy. In such a way that when the Rock has fallen 12 [m] it is located 8 [m] from the ground level.
m*g*h = 0.5*m*v²
v² = (g*h)/0.5
v = √(9.81*8)/0.5
v = 12.52 [m/s]
The kinetic energy of an object of mass m moving with speed v is given by:
For the bicycle in our problem,
and
, so the kinetic energy is
The formula for a kinetic energy KE of a falling body is
KE = mgh
where m = mass, g = acceleration due to gravity (9.8 m/s^2, constant), h = height.
The total mass of a skateboader and a skateboard is 64 + 2.0 = 66 kg.
Finally,
KE = 66*9.8*5.0 = 32340 J
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Answer: Something that's vibrating, and you also need medium for those vibrations to start in.
I hope this helped!
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- Zack Slocum
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