Answer:
2)Ek = 686.7[J]; 4) see the explanation part; 5) B) Remained motionless; 6) P = 339 [watt]
Explanation:
2)
Using, the principle of energy conservation we can find the kinetic energy of the rock. We must bear in mind that the potential energy as the rock falls is becoming kinetic energy.
[tex]E_{p}=E_{k}\\E_{p}=m*g*h\\where:\\m = mass = 1[kg]\\g=gravity=9.81[m/s^2]\\h=elevation[m]\\[/tex]
Now replacing the values:
[tex]E_{p}=1*9.81*(90-20)\\E_{p}=686.7[J]\\Therefore\\E_{k}=686.7[J][/tex]
4)
- False, the work is always done in the same direction as the application of force.
- True, energy is always conserved and transformed from one form to another, that is why the sum of potential and kinetic energies will remain constant.
- False, the moment is defined as the change of speed in a body, under the effect of force in a time interval.
- False, the kinetic energy is increasing, while the potential energy is decreasing
5)
B) Remained motionless
The reason is that work is defined as the product of force by distance, when there is no work for this case, it is because there is no movement of the object due to force.
6)
We recall that work is defined as the product of force by distance
W = F * d
W = 113 * 27
W = 3051[J]
And power is defined as the amount of work performed over a time interval.
Power = W/t
Power = 3051/9
Power = 339 [watt]
