if they say: If the block starts from rest 12.0 m up the plane from its base, what will be .....
where is the 12.0m leg?

Question

if they say: If the block starts from rest 12.0 m up the plane from its base, what will be .....
where is the 12.0m leg?

loser66 · Answer

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loser66 · Answer

@e.mccormick

loser66 · Answer

AB or AC?

loser66 · Answer

Problem 48

e.mccormick · Answer

I think it is BC, but I have not found a single reference.

loser66 · Answer

you mean you are not sure?

e.mccormick · Answer

Never took physics.

loser66 · Answer

that's why I don't ask you physics, I ask you English. right? hehehe.

e.mccormick · Answer

Yep.  Or some of computer science.  Hehe.

loser66 · Answer

wait for me,  I will not let you free next semester when I take computer science.

e.mccormick · Answer

Hehe.  I'll be sure to forget it all by then.

ybarrap · Answer

"The block starts from rest 120 m up the plane from it's base" means that the block is perpendicular to the floor (i.e. the ground plane, where it's base is located). So $\overline{AB}=120~m$.

loser66 · Answer

@ybarrap  so, I have to use tan $\theta$ to find out AC and then apply AC = 1/2at^2 as it moves horizontal direction, ignore BC, right?

ybarrap · Answer

I meant 12.0 m, not 120 m.  AB = 1/2 at^2. The vertical drop will be like free fall with nothing to slow it down, like friction.

e.mccormick · Answer

Never would have guessed AB since they define "the plane" as BC.

(II) The block shown in Fig. 4-43 has mass m = 7.0 kg and lies on a fixed smooth frictionless plane tilted at an angle $\theta = 22.0^\circ$ to the horizontal. (a) Determine the acceleration of the block as it slides down the plane. (b) If the block starts from rest 12.0 m up the plane from its base, what will be the block's speed when it reaches the bottom of the incline?

ybarrap · Answer

I think you are right, I did not read that part carefully. It slides "down the plane" and it is 12.0 m "up the plane" @e.mccormick makes sense. I would agree.

ybarrap · Answer

I still think AB = 1/2 at^2. The vertical drop will be like free fall with nothing to slow it down, like friction.

loser66 · Answer

@ybarrap  I understand what you mean. the time for the object go from B to C is calculated by vertical direction which is the same if we calculate via horizontal direction. I just want to figure out what is 12.0 m length. Obviously, if I go backward and say AC =12, my answer goes wrong.

ybarrap · Answer

No, we think that BC=12.0 m.

loser66 · Answer

whaaatt? you confused me. why BC?

loser66 · Answer

oh, oh, I got you. heheh. sorry friend

ybarrap · Answer

No problem. The question is not very clear, but that BC = 12.0 makes the most sense.

loser66 · Answer

got you, thank you