Posted by Jon on Tuesday, April 1, 2008 at 10:16am.
14)The cable of the elevator you are riding in breaks and the elevator begins to freefall at terminal velocity to the ground. Why would jumping up right before impact still not help you survive?
A)Because your overall inertia is down
B)Because you would be accelerating up
C)Because you are weightless
D)It would help you survive
I got C
15)If a horizontal force applied on a resting object is greater than the force of friction, the object will.
A)move at a constant velocity
B)accelerate in the direction of the applied force
D)stay at rest
I got B
- physics - sonia, Tuesday, April 1, 2008 at 10:53am
14)da ans is a
- physics(2nd opinions please) - Jon, Tuesday, April 1, 2008 at 11:09am
anyone else agree?
- physics - Count Iblis, Tuesday, April 1, 2008 at 11:37am
In 14 the best answer is D, although in it won't work well.
By jumping up you reduce the velocity w.r.t. to the ground a bit, so when the bottom of the lift hits the ground and stops, you are moving toward the ground at a lower speed.
In 15 all options are wrong. You are supposed to answer B) but strictly speaking that is not right because the applied force does not need to point in the direction opposite to the friction force.
- physics - drwls, Tuesday, April 1, 2008 at 1:51pm
I agree with Iblis on 14. You can slightly reduce your velocity relative to the Earth at impact by jumping up just before impact. The effect might be helpful when falling one story, but not much more than that, or when the elevator is falling at terminal velocity (as here), which would be huge. They probably want you to answer A
In 15, Iblis is refering to the possiblity of friction with a directional bias, such as one might abtain when sliding on a grooved surface where the groves are inclined to the applied force. They want you to answer B, but is not always true.
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