woodyapex Posted June 9, 2011 Share Posted June 9, 2011 Im sure this is a simple calculation but ! An object weighing 300 kg is dropped off a ledge 6 m high ! how fast would it be travelling when it hits the ground ? i realize weight at this point is not too much of a issue but when i get an answer to this , i weight will be for my next question! Thanks in advance ! Link to comment Share on other sites More sharing options...
Sato Posted June 9, 2011 Share Posted June 9, 2011 It will fall at a constant rate of 9.8 meters per second, I'm assuming that air resistance won't be factored in. Link to comment Share on other sites More sharing options...
woodyapex Posted June 9, 2011 Author Share Posted June 9, 2011 It will fall at a constant rate of 9.8 meters per second, I'm assuming that air resistance won't be factored in. 9.8m per second ? sato what about excelaration or have you factored that in ? im looking for the speed its doing when it hits the ground ? is it still 9.8 m per second ? thanks Link to comment Share on other sites More sharing options...
mooeypoo Posted June 9, 2011 Share Posted June 9, 2011 ! Moderator Note Moved to homework help. Remember, we help lead towards the answer, we do not give the answer away. Link to comment Share on other sites More sharing options...
Sato Posted June 10, 2011 Share Posted June 10, 2011 9.8m per second ? sato what about excelaration or have you factored that in ? im looking for the speed its doing when it hits the ground ? is it still 9.8 m per second ? thanks If you dropped it 9.8m instead of 6m, then the object would hit the ground in a second. No matter an objects shape, size, or weight, it will remain falling at a constant rate of 9.8 meters per second until it hits the terminal velocity. Since your object only falls for 6 meters, it should hit the ground in about 61 milliseconds. Link to comment Share on other sites More sharing options...
sam123 Posted June 10, 2011 Share Posted June 10, 2011 9.8 is not the speed, it is the acceleration.... Potential energy at the top is equal to the kinetic energy at the bottom. 1/2 x m x v2 = mgh Substitute and find v which is the speed of the ball at the bottom. Hope it helps... Link to comment Share on other sites More sharing options...
imatfaal Posted June 10, 2011 Share Posted June 10, 2011 I would go along with Sam (and not with Sato!) - alternatively you could use the standard equations of motion and look for one that relates initial velocity, final velocity, acceleration, and distance. These will give the same result (phew!) Link to comment Share on other sites More sharing options...
mooeypoo Posted June 10, 2011 Share Posted June 10, 2011 It will fall at a constant rate of 9.8 meters per second, I'm assuming that air resistance won't be factored in. It will fall at a constant acceleration of 9.8 meters per second squared. If you know the initial velocity (zero) and you know the height, you have the acceleration, you can calculate the final velocity easily from the equations of motion. You could also use energies to solve it (initial=final), but I am not sure which one you need to use in this exercise more. In any case, beware of units. Acceleration (m/s^2) is not the same as speed (m/s). Link to comment Share on other sites More sharing options...
woodyapex Posted June 10, 2011 Author Share Posted June 10, 2011 It will fall at a constant acceleration of 9.8 meters per second squared. If you know the initial velocity (zero) and you know the height, you have the acceleration, you can calculate the final velocity easily from the equations of motion. You could also use energies to solve it (initial=final), but I am not sure which one you need to use in this exercise more. In any case, beware of units. Acceleration (m/s^2) is not the same as speed (m/s). the formulas are losing me a little as its chuffing ages since i did them at school ! i realize it will take .62 of a second i think ?? to hit the ground but where do i put that in the formula ? Link to comment Share on other sites More sharing options...
mooeypoo Posted June 10, 2011 Share Posted June 10, 2011 Can you post how you started your formulas, woodyapex? I can help more if I see where you got stuck. Link to comment Share on other sites More sharing options...
woodyapex Posted June 10, 2011 Author Share Posted June 10, 2011 Mooey poo I have got to be honest there is a hell of a lot more to this then what ive put ! it is for a spcific event ive entered and besides the little problem ive put there is also a lot of wind drag ! now the long and short of it ive got to design a plane , build a plane ! got to talk to the press , sort out sponsorship , communicate with sponsors ,make a video diary ! oh and did i mention build a 8m long and wide plane ? I realize how your forum works now , but did not initially ! for the sake of a probably 10 second calculation i presumed one of your forum members may just work it out . and i'm sure they would ! I read how the " homework " forum works thats why i put it into the physics forum ! Don't worry about it as im sure you wont ill sort it out but i just don't have the time and at the min brain space to start from scratch on this subject ! thanks woody Can you post how you started your formulas, woodyapex? I can help more if I see where you got stuck. Link to comment Share on other sites More sharing options...
mooeypoo Posted June 10, 2011 Share Posted June 10, 2011 Mooey poo I have got to be honest there is a hell of a lot more to this then what ive put ! it is for a spcific event ive entered and besides the little problem ive put there is also a lot of wind drag ! Okay, let's take this one step at a time. First, don't panic Everything has a solution, and we can help you out with this. I just need to know what w're talking about in terms of the mechanics involved; if you have an object just in free-fall downwards with wind, we can solve it with forces on the x/y axis. But if it's a plane, then we have mixed effects from Bernoulli to drag and gliding. So we really need to set the context of this project and then we can help you. now the long and short of it ive got to design a plane , build a plane ! got to talk to the press , sort out sponsorship , communicate with sponsors ,make a video diary ! oh and did i mention build a 8m long and wide plane ? Awesome. Sounds like a fun project! I realize how your forum works now , but did not initially ! for the sake of a probably 10 second calculation i presumed one of your forum members may just work it out . and i'm sure they would ! I read how the " homework " forum works thats why i put it into the physics forum ! Don't worry about it as im sure you wont ill sort it out but i just don't have the time and at the min brain space to start from scratch on this subject ! thanks woody This isn't raelly about how the forum works, I read your question and thought it was more of a homework problem, which is why I transfered it to the HW forum. In here, we don't "feed" answers, we try to help you get the answers yourself so you can repeat the process later in exams or other projects. This sounds more like an engineering project. Quite a fun one, too. Depending on the way things go, we might switch it to the engineering forum instead, or, alternatively, you can post another thread in the Engineering forum and ask the *FULL* question this time We can help you but we really have to know what the context is.. there's a difference between helping a high school student solve physics homework problems about falling objects and a college student trying to do a lab or design an experiment, or a full blown engineering feat like what you're attempting. So, yeah, sorry if I moved it to the wrong place, but I think you should just post the whole requirement for your project and tell us what you already tried to do and where you got stuck so we can focus our attention on helping you finish it. If you only need the calculation, then again, just give me *all* the details; a free-falling object without air resistance use the equations of motions in 2D. IF there's air resistance, you need to calculate the new acceleration. If there's wind, you have another force sideways (or diagonal) which you need to break up. If it's a plane, though, you need to consider gliding as well. So even a 10 second calculation requires a bit more data. It's your choice what you want to do to proceed, but we need a tad more info to be able to help you out. The project sounds like a lot of fun, I hope you'll update us as to how it goes, though, regardless! ~mooey Link to comment Share on other sites More sharing options...
mooeypoo Posted June 13, 2011 Share Posted June 13, 2011 I created a new thread for the full project in Engineering with that last post you posted (explaining the project itself). You will likely get much more help there. I'll go over it myself later, I must run now, but good *luck*!!!!! Link to comment Share on other sites More sharing options...
rktpro Posted June 13, 2011 Share Posted June 13, 2011 Im sure this is a simple calculation but ! An object weighing 300 kg is dropped off a ledge 6 m high ! how fast would it be travelling when it hits the ground ? i realize weight at this point is not too much of a issue but when i get an answer to this , i weight will be for my next question! Thanks in advance ! Here, You should not consider the weight of object as every object has same acceleration on 9.8m/S2 . Look, the object is dropped with zero initial velocity. And the final velocity would be, say=u, since we have to calculate it. Now you know the acceleration which is constant for every object falling freely. Note that you have to consider air resistance as zero unless you are ready to do more complex calculations and you want the precise and striking exact speed. But, that would be a mess since you would have to measure air speed, atmospheric pressure etc. Now, back to problem. You now have three quantities. Let us add one more. We know the height=6m. Now it is simplified. Use the equation of motion. Which one? I bet you know that! Link to comment Share on other sites More sharing options...
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