mcat question of the day june 7

[naphthalene]

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A triangular ramp has a width of 3 meters and height of 4 meters. If the height of the ramp increases to 12 meters while maintaining the same width, how much more work is required to bring an object from the ground to the top of the ramp?

(a) 1 times more work
(b) 2 times more work
(c) 3 times more work
(d) 4 times more work


I thought that the amount of work does not change?? only the force required changes....... please help!

 

[ridethecliche]

3x the height = 3x the work.

Formula = mad

Mass and acceleration are the same. Distance increases 3x.

 

[wasvsdal]

Work = Force (Distance), so if the force was to change then the amount of work would change as well. But in this case, its the distance that is changing, and not the force. And since work and distance are directly proportional, they both increase by 3x.

 

[naphthalene]

I did a question where there was no ramp vs. ramp and the amount of work stayed the same because machines don't change the amount of work required. So i am a little confused, since the work would be the same without ramp and ramp, but the work also changes when the distance/height of the ramp changes..

 

[SeminoleVesicle]

W=Fd...we're talking about vertical distance here.

 

[whiteshadodw]

first time: mgh(0 meters) + Work = mgh (4 meters)
second time: mgh(0 meters) + work = mgh (12 meters)

mg*12 meters / mg*4 meters = 12 meters / 4 meters = 3x as much work. this is assuming a frictionless system.

 

[ridethecliche]

I did a question where there was no ramp vs. ramp and the amount of work stayed the same because machines don't change the amount of work required. So i am a little confused, since the work would be the same without ramp and ramp, but the work also changes when the distance/height of the ramp changes..

I bet you that the distance moved by the object was the same.

The only force opposing the movement of the object is gravity. So lifting it straight up to 3m and rolling it up a ramp to a height of 3m requires the exactly same amount of work. The forces change, i.e. the ramp requires less force and more time.

Your fundamentals aren't solid. The two problems are asking different things. It's nice to fall back on previous problems, but you really have to figure out what they are asking before you can compare them. You seem to be assigning the formula terms and concepts to the wrong entities. I.e. distance traveled (ramp) instead of distance moved that is opposite to the opposing force (gravity). We are ignoring friction here.