Сообщение №4260 от ghdghdg , 12 апреля 2009 г. 22:38:
В ответ на №4243: Help with some physics problems от Kristin , 16 февраля 2009 г.:
> I am trying to understand these and hoping that someone can explain them.
> 1. How much work does a person do to lift 60000g a distance of 7.8 ft in 10s? How much power? Hp? work = f(delta)d d (represents displacement) therefore60kg*9.8m/s2(gravity is considered cause its being lifted off ground)* 7.8 ft (the displacement) = 4586.4 J but that is incorrect, because you have to convert the ft into meteres, when u do that, then u will get the right answer, reason for this is u have to use standard units, wat grade is this by the way? Power = to W / t (or time) power= 4586.4 J / 36,000 seconds (s is standard unit and u have to use it) = 0.127 W which is still wrong, because i used the value of 4586.4 J which had ft, you have to change the ft into meters, then if you follow the steps above, you will get it right Horsepower, is ugh... i cant remember top off my head 786 W or 786 Kw i dont know, but which ever one you get just divide it by the horsepower. > 2. What is the average speed in m/s of an airplane that flies 6000 miles in 10 hrs? avg speed = total speed over total time therefore6000 miles / 10 hours =600miles/hour or if you wish to convert it to seconds, divide it by 3600> 3. What is the speed of a 784N person that expends 2260 J of K.E.? I dont kno about this one sorry, you dont have enough to answer it, i think. the two equations i know that MIGHT work are Energy is equal to mgh and .5mv(square the v) you know the total energy is 2260 J therefore2260 J = to .5mv(squared) v2= .5m/ 2260 J v = (.5m / 2260 J) squarerootThats as far as i can get, and this is due to the fact that mass is missing, if you have any questions you could ask me at ebro.husaini@gmail.com, but please do answer this, wat grade of physics is this? cause im learning this stuff in grade 11, and if you guys are learning it in a previous year, thennn mayb i should study at russia