In summary, the four given questions involve applying Newton's second law, F = ma, to solve for either force or acceleration. Each question provides two known values and one unknown, which can be substituted into the formula to find the missing variable. It is important to draw a free body diagram and consider the direction of forces when adding them together. Additionally, for the elevator problems, it is important to note that most of the time, the elevator is not accelerating and the person's weight remains constant. Understanding the principles behind the equations can help in solving the problems more accurately.
Again draw the forces ON the lawnmower. You have the weight which acts down. The push on the handle which acts diagonally DOWN from the middle of the mower and there is an upward force of the ground on the mower. You draw the friction parallel to the ground and in the backward direction.
Since the mower is moving parallel to level ground you are only concerned with forces that act parallel to the ground. How many do you have? Well obviously friction but is there another one? If so what is it?
#38
mrphobio
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So sin? because this is where i am confused. I don't know if i want to find the hypotinus or the just left to right force
#39
netgypsy
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Only forces that are parallel to the ground aka left and right
sin will give you a downward force So what's left to use?
You want the total force applied by the student, so that'd have to be the hypotenuse. But you'll have to find the parallel forces first.
#41
mrphobio
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okay. So i want to find the force that is parrelel to the ground (other then friction). So to use one of the sin, cos, tan i need another side to the triangle. Would it be the 14.9kg that is pushing the lawnmower down?
#42
netgypsy
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In other words you can find the parallel force first, then use the trig function to find the diagonal if you wish or you can do it all in one equation.
The sum of the forces in the x direction equal mass times acceleration. One force moves the mower, the other holds it back.
Nope - the weight is vertical. You don't need it in this problem to figure out the horizontal motion since friction is already given
What's the only thing you don't know?
#43
netgypsy
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You can use the letter F for a force you don't know.
#44
mrphobio
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If the sum of the forces in the x direction equal mass time acceleration, then that would mean 12.9*3.7=47.73. But that's less then the friction.. so wouldn't that mean that it is not moving?
#45
netgypsy
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Think of it this way. When you push a lawn mower your push does two things. It actually makes the mower feel heavier because part of your push is downward. It makes the mower accelerate because it moves it forward
#46
netgypsy
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OK your equation will be Force of the push in the x direction minus force of friction equals mass times acceleration
#47
netgypsy
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You know all of this but the force of the push in the x direction so just put a letter in for that force. Like Fx
#48
netgypsy
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Once you find that you can use your trig functions to find the diagonal force (hypotenuse)
#49
mrphobio
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Fx-Ff=ma... So i know Fx-68=12.9*3.7
#50
netgypsy
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right! Now just solve for Fx
#51
mrphobio
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115.73 Now is this when i plug into cos? cos(28)=115.73/x (with x=hypotinus)
#52
netgypsy
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You got it. Check your math. Good JOB
#53
mrphobio
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Sick! i can't thank you enough. I would of got none of the equations right if it weren't for this. Website crashed again (probably because of all the kids doing homework last minute) but ill get it in as soon as it is up! thanks again and good night.
#54
netgypsy
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Did you get number 2? It works like number 1 but don't forget to calculate the total mass and the total actual weight before you sum your forces.
Good luck
#55
mrphobio
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Yah i got number 2. I was able to figure it out all by myself :D. Drawing things out makes it sooooo much easier.
#56
netgypsy
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Tell me about it. I flunked my first physics courss (took it over and got an A though)
#57
mrphobio
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i did the 70kg times the 20 (because it was the maxium occupancy). and then added the answer to that to 540kg to get the total down force. I converted it to Newtons then subtracted the up force (32471) from the down force. With that, I did F=Ma and got the answer. hopefully that made sense haha