The law of conservation of energy and energy efficiency!!!!!!!Can you please answer the following questions, show clear working out, and please...

1. Kinetic energy will be needed raise body and speed when
leaving the ground?

When the body of mass m = 55 kg is
raised by height h = 0.8 m. The increase in potential energy (e) is given by the
formula:

e = m*h*g

Where g =
acceleration due to gravity = 9.81 m/s^2

Applying value for
given variables in the above formula:

e = 55*0.8*9.81 =
431.64 J

Kinetic energy of an object is given by the
formula:

e =
(1/2)*m*(v^2)

When v represent the velocity required to
enable the athlete to attain the the potential energy this kinetic energy will be equal
to the potential
energy:

Thus:

431.64 =
(1/2)*55*(v^2)

Therefore:

v^2
= 431.64*2/55 =
15.696

And:

v =
3.962 m/s

2.  Given a power input of 400 watts, calculate
the efficiency of devices that produce outputs of:

a) 80
watts

Efficiency = (80/400)*100 =
20%

b) 300 watts

Efficiency =
(300/400)*100 = 75%

3. A catapult stores 25j of elastic
potential energy, but the projectile that fires has a kinetic energy of only 15j. What
is the catapults efficiency?

Efficiency = (15/25)*100 =
60%

4. If the electric motor of a forklift has an
efficiency of 90% how much energy is needed to increase a crates gravitational potential
energy by 2000j?

Energy needed = (Potential
energy)*100/Efficiency

= 2000*100/90 = 2222.2222
J

5. In a torch, the efficiency of a battery in converting
chemical to electrical energy is 85%, and the efficiency of the globe in converting
electrical into light energy is only 2%. What is the overall
efficiency?

Overall efficiency = (Chemical
efficiency)*(Globe efficiency/100

= 85*2/100 =
1.7%