Time + power - practice problems - page 3 of 5
Number of problems found: 84
- Electric work
Calculate the work done by the electric forces passing the current of 0.2 A through the bulb in 10 minutes if the bulb is connected to a 230 V power supply. - Resistance 25021
Calculate the resistance and power of the appliance through which a current of 20mA flows at the mains voltage (230 V). - Quiz or test
I have a quiz with 20 questions. Each question has four multiple-choice answers, A, B, C, D. THERE IS NO WAY TO KNOW THE CORRECT ANSWER OF ANY GIVEN QUESTION, but the answers are static, in that if the "correct" answer to ; 1 = C, then it will always be e - The half life
The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half its initial mass. Starting with 145 grams of a radioactive isotope, how much will be left after three half-lives?
- Energy consumption
The device is connected to 230V and draws a 3.5A current. Power consumption is 1932kJ. How many minutes has this device been in operation? - Transformer 20073
The transformer is oil-cooled and transforms a power of 20MW with an efficiency of 92%. Determine the temperature of the oil at the outlet of the transformer if the oil was 20°C when it entered the transformer. 2.5 liters of oil will flow through the tran - Surroundings 19153
A heating element with a resistance of 1.6 Ω is used to heat the car's rear glass. The body is connected to the battery in the car, which has a voltage of 12 V. a) What is the power input of the heating element? b) How much heat does the heating element g - Cylindrical 16713
Twenty identical steel balls were dropped into a cylindrical container of water standing on a horizontal surface to submerge them below the surface. At the same time, the water level rose by 4 mm. Determine the radius of one sphere if the diameter of the - Worker's performance
Fifteen workers paint 180 m fence in 3 days. In how many days will nine workers paint a 360 m fence? We assume that each worker has the same, constant and unchangeable performance.
- 3 phase load
Two wattmeters are connected to measure power in a 3 phase balanced load. Determine the total power and power factor if the two wattmeters read 1000 watts each (1) both positive and (2) the second reading is negative. - The mowers
The mowers were to mow two meadows, one twice as big as the other. They divided into two equal groups in the first half of the day. One continued to mow a larger meadow and cut it all by the end of the day. The second group mowed a smaller meadow but did - Friction coefficient
What is the weight of a car when it moves on a horizontal road at a speed of v = 50 km/h at engine power P = 7 kW? The friction coefficient is 0.07 - Four pavers
Four pavers would pave the square in 18 days. How many pavers do you need to add to the done work in 12 days? - Power input
The construction lift lifted a load weighing 300 kg to a height of 12 m with a uniform movement. How long has it taken for the load to be lifted if the efficiency is 75% and the engine has a power input of 5 kW?
- Performance 7737
Zdenek, weighing 54 kg, made 15 push-ups on the crossbar. The height he reached was about 40 cm. What kind of work did he do? What was his performance if the whole exercise took him a minute and a half? - Two pipes
How long will the pool be filled with a double supply pipe if it takes the pool to fill the first pipe by 4 hours long and the second pipe 9 hours longer than both pipes open simultaneously? - Temperature 7595
Colorless liquid weighing m = 200 g is heated with constant stirring on a stove with power input P0 = 600W. 80% of the supplied energy is used to heat the liquid. Selected measured values of liquid temperature as a function of time are recorded in the t - Two friends
Peter can do all his work himself in 6 hours. Martin can do the same work himself in 8 hours. Peter worked first and was then replaced by Martin. The whole work was done in 6.5 hours. Calculate how long Peter worked before being replaced by Martin. - Three machines
The power of the three machines is 2:3:5. Two most powerful machines produce 400 parts per hour. How many components make all three machines in 3 hours?
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