Electrotechnology 2
ELC260S
Tutorial problems – Basic Concepts and Calculations
1) A force of 1648 N is needed to push a motor. Determine the work done when
this motor is pushed over a distance of 12,5m.
i. (20,6 kJ)
2) An electrical motor is lifted through a height of 6m, 2355 J is required for this
process. Calculate the mass of the motor.
i. (40 kg)
3) A force of 690 N is applied over a distance of 150m, in the direction of the
applied force. The distance is covered in 5 minutes. Determine the power.
i. (345 W)
4) A mass of 350 kg must be lifted with a hoist. The drum has a diameter of
0,45m and a rotational frequency of 164 r/min. Find the input power if the
system has an efficiency of 78%. Determine the cost to operate the hoist 5
hours per day, 21 days per month.
i. (17 kW, R 624,75)
5) A hoist is supplied with 4,5 kW to lift a bucket containing 20,5 ℓ of water.
Determine the rotational frequency if the hoist has a drum with a radius of
0,275m.
i. (777 r/min)
6) The winch on the front of a 4x4 bakkie is supplied with 12V and a maximum
current of 45 A. The winch pulley has a radius of 8,5 cm and a maximum
tensile force of 12450 N. Determine the rotational frequency of the winch for
these conditions
i. (4,873 r/min)
7) Determine the heat required to raise the temperature of a copper object, with a
mass of 50 kg from 15 ºC to 45 ºC. The heating process takes 4 minutes, and
50 of these objects must be heated. Determine the total cost.
i. (585 kJ, R 2,84)
8) An aluminium casting must be heated from 21 C to 56 C in a period of 3
minutes. Determine the maximum mass of each casting if the furnace is
supplied with 1,75 kW.
i. (9,47 kg)
9) A 2 kW kettle with an efficiency of 92 % is used to heat 1,25 kg of tap water
from 16 C to 96C. Determine the time taken to complete the heating, and the
cost.
(3 min 47,7 s, 4,4 c)
Due date:
02 March 2022