Answer:
a) F=20 [kgm/s^2]=20 [N]
b) W=100[kgm^2/s^2]=100[J]
c) P=44,84[kgm^2/s^3]=44,84[W]
d) W=2,778*10^-5 [kilowatt-hours]
Explanation:
a) Newton's Second Law states that <em>the acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force and inversely proportional to the mass of the object.</em>
F=ma
where:
- F, the net force [N]
- m, mass of the object [kg]
- a, acceleration [m/s^2]
If a 10 kg mass is lifted with an upward acceleration of 2 m/s^2, the upward force necessary is:
F=10 [kg]*2[m/s^2]=20 [kgm/s^2]=20 [N]
b) The amount of energy required to lift the box equals the magnitud of work done by the lifting force:
W=FdcosФ
where:
- W, work executed [J]
- F, net force [N]
- d, displacement produced by the force [m]
- Ф, angle between the net force and displacemt produced
Thus, the energy required to lift 5 m the mass is:
W=20[N]*5[m]cos0°=100[N.m]=100[kgm^2/s^2]=100[J]
c) To find the average power we use the formula:
P=W/t
where,
- P, average power [W]
- W, work executed [J]
- t, elapsed time [s]
Thus, if the process takes 2,23 seconds the average power is:
P=100[J]/2,23[s]=44,84[J/s]=44,84[kgm^2/s^3]=44,84[W]
d) As 1 kilowatt-hours=3,6*10^6 J, then:
100 [J]*1 [kilowatt-hour]/ 3,6*10^6 [J]=2,778*10^-5 [kilowatt-hours]
