Question

Бетонную балку массой 3 т равномерно подняли на высоту 5 м, совершив для этого работу 160 кДж. Какая работа затрачена на преодоление силы трения? Каков коэффициент полезного действия механизма? (принять g≈10 Н/кг). Ответ: (округли до целого числа)

Answer 1

Дано:                                СИ:                         Решение: m=3т                                m=3 000кг                η=Ап/Аз*100%Aз=160кДж                        Aз=160 000Дж          Ап=gmh g=9.8                                                                Aп=3 000*9.8*5=150 000Дж h=5м                                                               η=150 000/160 000*100%=93.75%_______________________________________Ат=Аз-Ап   Ат=160 000-150 000=10 000ДжОтвет:η=93.75%;Ат(работа на трение)=10 000Дж

Answer 2

Calculation of Work Done to Lift the Concrete Beam

To calculate the work done to lift the concrete beam, we can use the formula:

Work = Force × Distance

Given: - Mass of the concrete beam = 3 t (tonnes) - Height lifted = 5 m - Work done = 160 kJ (kilojoules) - Acceleration due to gravity (g) ≈ 10 N/kg

First, let's convert the mass of the concrete beam from tonnes to kilograms: 1 tonne = 1000 kg

So, the mass of the concrete beam is: 3 t × 1000 kg/t = 3000 kg

Next, we can calculate the force required to lift the concrete beam using the formula: Force = Mass × Acceleration due to gravity

Force = 3000 kg × 10 N/kg = 30000 N

Now, we can calculate the work done to lift the concrete beam: Work = Force × Distance Work = 30000 N × 5 m = 150000 J (joules)

Since the given work is in kilojoules, we need to convert it to joules: 1 kJ = 1000 J

So, the work done to lift the concrete beam is: 150000 J = 150 kJ

Therefore, the work done to lift the concrete beam is 150 kJ.

Calculation of Work Done to Overcome Friction

To calculate the work done to overcome the force of friction, we need to know the coefficient of friction and the distance over which the force is applied. Unfortunately, the coefficient of friction and the distance are not provided in the question. Without this information, it is not possible to calculate the work done to overcome the force of friction.

Calculation of Efficiency (Coefficient of Useful Work)

The efficiency or coefficient of useful work (η) of a mechanism is defined as the ratio of the useful work output to the total work input. It can be calculated using the formula:

Efficiency (η) = (Useful work output / Total work input) × 100%

In this case, the useful work output is the work done to lift the concrete beam, which is 150 kJ (as calculated earlier).

The total work input is the work done to lift the concrete beam plus the work done to overcome the force of friction. Since we don't have the value for the work done to overcome friction, we cannot calculate the total work input.

Therefore, without the information about the work done to overcome friction, it is not possible to calculate the efficiency or coefficient of useful work of the mechanism.