External force.
Air resistance, friction, grass rubbing on a rolling ball, etc.
If there is no external force on a moving object, it keeps going.
Forever !
Answer:
Correct answer: Third statement P = 4900 W
Explanation:
Given:
m = 500 kg the mass of the elevator
h = 10 m reached height after t = 10 seconds
P = ? power of the motor
The formula for the calculating power of the motor is:
P = W / t
since work is a measure of change in this case of potential energy then it is:
W = ΔEp = Ep - 0 = Ep
In this case we must take g = 9.81 m/s²
Ep = m g h = 500 · 9.81 · 10 = 49,050 W ≈ 49,000 W
Ep ≈ 49,000 W
P = Ep / t = 49,000 / 10 = 4,900 W
P =4,900 W
God is with you!!!
Answer:2.541
Explanation:
Well , Potential Energy = mgh
m=mass = 82
g=acceleration of gravity=9.80m/s^2
h=what we are looking for
PE=mgh
PE/(mg) = h
Substitute in the values:
1970/(82 x 9.8) = h 2.541
Explanation:
It is given that,
Mass of the football player, m = 92 kg
Velocity of player, v = 5 m/s
Time taken, t = 10 s
(1) We need to find the original kinetic energy of the player. It is given by :
k = 1150 J
In two significant figure, 
(2) We know that work done is equal to the change in kinetic energy. Work done per unit time is called power of the player. We need to find the average power required to stop him. So, his final velocity v = 0
i.e. 
P = 115 watts
In two significant figures, 
Hence, this is the required solution.
Wind turbines work on a simple principle: instead of using electricity to make wind—like a fan—wind turbines use wind to make electricity. Wind turns the propeller-like blades of a turbine around a rotor, which spins a generator, which creates electricity.
