# Work and power

1. Nov 29, 2014

### Fabian901

If Power = Force x Distance / Time, does that mean that if we apply the same force on 2 objects with different masses and we apply the force across the same distance, the object with the lower mass will have a higher power?. The way I'm looking at this is that the object with the lower mass will have a higher acceleration (a = F/m) and therefore reach distance "D" faster than the object with the higher mass. Please correct me if I am wrong as I don't want to go to the next topic without fully understanding this concept.

2. Nov 29, 2014

### Bystander

Higher power was used to accelerate the lower mass. I wouldn't say the lower mass has a higher power.

3. Nov 29, 2014

### dean barry

The energy consumption is the same

4. Nov 29, 2014

### sophiecentaur

The two masses will end up with the same kinetic energy (same force applied times distance). The smaller mass will end up at the end of travel quicker - because the acceleration will be greater. Power is rate of doing work and it is zero if no work is being done, so neither of the masses will 'have' any power at the end. They will be expending 'no power' after being launched. The energy is delivered to the smaller mass faster so the Power is higher- but for a shorter time, of course and Energy is Power times Time.
It pays to be very strict with your use of terms in Physics because they each have specific meanings and applications. Also, there are often alternative ways of approaching problems like this one. It's worth bearing in mind that this sort of problem is often the best approached by energy considerations rather than speed considerations. Here, the simple fact that Energy is the same in both cases, tells you the answer without bothering with working out the acceleration at all (which is not wrong, of course - it just saves time).

5. Nov 29, 2014

### Fabian901

I see, and why is this concept important in mechanics? How does it apply to wind energy for example? Or water power?

6. Nov 29, 2014

### Staff: Mentor

There are lots of scenarios where it may be important. It is part of the reason why a lighter car would be faster and more efficient than a heavier one, for example.

I can't think of a reason why it would come into play with wind and hydro power though....is there some context to that question?

7. Nov 29, 2014

### sophiecentaur

Which concept are you referring to? I have mentioned several. :)

8. Nov 29, 2014

### Fabian901

I'm referring to the concept of power, in which scenario will it be important to calculate power? If you can give me a scenario related to mechanical engineering then that would be better :)

9. Nov 29, 2014

### Fabian901

I have to learn the advantages and disadvantages of using wind power, water power and solar power but I'm just curious as to how they would measure power in wind energy. Perhaps its simply the rate at which kinetic energy of the air is converted into electrical energy but I'm not 100% sure

10. Nov 29, 2014

### PeroK

I guess you don't watch the F1 motor racing?

11. Nov 29, 2014

### Fabian901

Nope, I'm more of a tennis and nba basketball fan. How would power relate to F1 racing? I've always heard the term horsepower which is equal to 746 Watts but I'm not sure what it represents. Is it simply the amount of jules transmitted per second from the engine to the wheels of the F1 car?

12. Nov 29, 2014

### PeroK

Yes, Power is Energy per second. Horsepower is a measure of power based on the power of an average horse! Try Googling it.

Note that the unit of energy is the Joule (not the jule).

13. Nov 29, 2014

### Bystander

In watts, same as any other power (or horsepower if you prefer --- some might prefer Dalton-furlongs2 per fortnight3, but it's a little awkward for most of us.)

Energy type "a" to energy type "b" is an efficiency.

14. Nov 30, 2014

### sophiecentaur

Power (P) is important when you are concerned with how quickly a particular job can be done, or the rate of work - for instance, how long it takes to gat a truck up a hill or a car to 100mph or how many tons of coal can be raised in an hour. That's Energy / time (Joules per second) (E/t) which has the unit of Watts.
Electrical heaters and motors are rated in Watts, to tell you the rate of heating, drilling, cutting etc.
Power in vehicles is very relevant, of course, but they tend to operate at variable speeds and acceleration so the actual output power of your engine can be anything from zero to (occasionally) maximum.
At the end of a job, the total Energy delivered will be the sum of the Pt for all the intervals of time at different output P values. That's what your Electrical Energy Meter calculates when it charges you for the Energy used or it will relate to how much furl you need to put in the fuel tank. (Naturally, the Efficiency of the engine / motor needs to be taken into account.
It is a good idea to get used to the Maths of the business; it is not a difficult bit of mathematical Physics,

15. Dec 1, 2014

### Fabian901

I see! Thanks a lot for the help everyone :)