Given that,
Electrical energy of the motor = 2280 J
Kinetic energy = 1606 J
Wasted energy in thermal and sound energy = 550 J
To find,
The efficiency of the motor in percent.
Solution,
Efficiency is defined as the ratio of useful output energy to the total energy.
Total energy = 2280 J
Useful energy = 1606 J
So, the efficiency of the motor is 70.43%.
Refer to the diagram shown below.
At A, the boy begins walking up the stairs.
At B, the boy is at the top of the slide. He has acquired PE (potential energy).
The value of the PE is
(50 kg)*(9.8 m/s²)*(11.5 m) = 5635 J
At C, the boy has KE (kinetic energy).
The value of the KE is
(1/2)*(50 kg)*(12 m/s)² = 3600 J
Energy is lost between B and C due to friction.
The lost energy is
5635 - 3600 = 2035 J
The distance traveled along the slide is 108 m.
If F = the average frictional force, then
(F N)*(108 m) = 2035 J
F = 18.84 N
Answers:
(a) The mechanical energy lost by sliding is 2035 J.
(b) The average frictional force is 18.84 N
The train would need the greatest amount of force due to weight! If you think of it, a baseball won't need much force to stop it, but if you have a heavy train, it will need excessive force to stop the train. The answer would be #3
I hope this answer helps!
Sorry if it doesn't make sense, as I don't know that much about physics! I am just thinking of what makes sense.
