How much horsepower does a 170 pound object have when it's moving 25mph?

Focus on the laws of motion.How much horsepower does a 170 pound object have when it's moving 25mph?
None. It takes no power to maintain that speed (on level ground, no friction). The object has kinetic energy (0.5 * m * v^2). Power was required to put it in motion and power can be recovered by decelerating it. If you do the math, the energy is 3551.86 ft-lb, equivalent to 1 horsepower for 6.458 seconds. Answer 1 neglected the fact that weight must be converted to mass by dividing by g, and energy is proportional to v^2.How much horsepower does a 170 pound object have when it's moving 25mph?
The best answer that I chose is...


Guitar_Junkie_





P.S. I made a mistake by putting this question to vote. Report Abuse

Your first mistake was the way you phrased your question. Now it seems you are asking about a force of 170 lb exerted at 25 mph (for instance moving your 170 lb object UPWARD at 25 mph), which Guitar_J answers correctly. Anyway, thanks for making the second mistake. Report Abuse

I thought if you were to exert a 170 pound object forward, then you put a load onto the wheels, it would put 11.33 horsepower out into the load, but I'm confused, because


';rahul_303'; said it will put out 12.79 horsepower, so which rating is correct? Report Abuse

horsepower is a RATE


the object moving has an AMOUNT of energy


Good thing you are a cop and not a physicist! Report Abuse

Oh S#隆鈥? you can still interpret law!!


Retire. Report Abuse

746 watts is equal to 1 horsepower


How much energy does 746 watts have?


Well, it depends on how long you apply it for.


Is a light bulb going on in your head?





You could legitimately ask; How many horsepower-hours is it equivalent to, but I expect you will just write a citation. Report Abuse

AP, re your followup question: Force and velocity are both vectors, meaning they have direction. The power is the force times the velocity times the cosine of the angle between their directions. A rolling object exerts a force (its weight) downwards, but travels horizontally. (continued) Report Abuse

What I thought...for example...If you had a 170 pound pile of bricks, then, you cranked it up on a spring, then pressed the ';release'; button, ...CONTINUES ON NEXT COMMENT... Report Abuse

...CONTINUING...%26amp; it accelerates to 25 mph. What you don't answer is...';HOW MUCH HORSEPOWER WOULD IT PUT OUT WHILE FREEWHEELING ON A FLAT GROUND BEFORE IT WILL COME TO A STOP???';. Report Abuse

(continued) This means the two vectors are at right angles so no power is needed (or exerted) to MAINTAIN that motion. When force and velocity are in the same direction, power is exerted and the object accelerates. So power is needed to ACHIEVE that motion. Report Abuse

NO, I'm not talking about the vectors...This thing that we're using to talk requires a limit of 300 characters, so I mean I have to split it up into 2. Anyway, to make it easy, how much horsepower would it take to get the 170 pound object going to 25mph in 1 second? Report Abuse

You can't say how much POWER it puts out while slowing due to friction unless you know the friction force (which is typically assumed to be constant no matter what the velocity is). Even then it's complicated because the power isn't constant, it decreases as the velocity decreases. (continued) Report Abuse

You can say how much kinetic ENERGY it has given its mass and velocity, that's 0.5*M*V^2, and it will lose all that energy when it finally stops. Report Abuse

Well, then how much horsepower would it have at peak speed (25mph)? Report Abuse

How much power to reach 25 mph in one second? Solve this:


P=KE/T (power, kinetic energy, time)


KE=0.5*M*V^2 (mass in slug, velocity in ft/sec)


M=W/G (weight in lb, grav. acceleration, = 32.17405 ft/sec^2)


P will be in ft-lb/sec. Divide by 550 to get hp. Report Abuse

Thanks, that's ALL I wanted to know.





Good bye. Report Abuse

How much hp would it have...? No answer. A horizontally coasting object doesn't have power, it has energy. Power is the rate of change of energy. Add friction (eg put on the brakes) and you do get power as energy is drained off; the brakes are dissipating power and getting hot. Report Abuse

Is that a P.S. Because I basically wanted the conversation to end, but you seem to want to start A new one. I'm talking about an object freewheeling from the laws of motion on flat ground. Report Abuse

If you get (for example) a bike as fast as you can get it going (with you on it), then even if you are on a flat ground, %26amp; you stop petaling, the bike can freewheel from the laws of motion (inercia). Report Abuse

Let's say that if it crashed into another object on wheels, that is a few pounds lighter, then the bike slows down, %26amp; other object starts to move because a moving object has tork (measured in HORSEPOWER). PROOF: Because it will start to push the other object on wheels (even while freewheeling). Report Abuse

Torque is not measured in horsepower. That is why a motor is rated in both units. Report Abuse

You would make a fantastic South Korean stem cell researcher. Report Abuse

Just make up a number that satisfies your will! Report Abuse

The only reason I continued the conversation was that the comments display doesn't update while you're typing a comment. While I was answering 'How much hp...' you wrote your bye-bye and posted it, but I didn't see it until after I posted my reply. Bye-bye. Report Abuse

O.K. Conversation ends here.





Note: 25 mph might not be as fast as you can (depends on what bike you're using).





2nd of all, I would recommend using a dummy in this experiment. Report Abuse

1 hp = 550 ft-lbf/sec





watch units





= 170 lbf * 36.67 ft/sec = 6233.9 ft-lbf/sec





6233.9/550 = 11.33 hp
Power is the rate of doing work. A such an object does not have ';horsepower'; or any other unit of power for that matter.





It will have energy though:





72.3 kg @ 11.111 m/s





Ek = 0.5 * 72.3 * 11.111^2 = 4463 J
12.79 horse power


follow the calculation





170 pound = 0.45 x 170 = 76.5 kilogram force


1 mile = 1852 meter


1 hour = 60 mins, 1 mins = 60 sec , 1hour = 60x60=3600sec


25 mph = 25 x 1852/3600 = 12.86 meter/sec





work require to move the object = weight x velocity


= 76.5 x 12.86 = 983.79 kgf-m





1 kgf.meter/sec = 0.013 metric horsepower





hence 983.79 kgf.meter/sec = 12.79 Horsepower(metric)





for conversion go to http://www.onlineconversion.com/





good luck,





rahul......
Power is the rate of doing work.





Power = Work done/Time (s)





Power = Watts = Joules/second in S.I. units





Work done = Force x Distance





Distance = Velocity x Time





Convert velocity of 25 mph into feet/minute





You can calculate it from there as horse power in Imperial units was defined in a previous question I answered.





Good luck.