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2] An elevator starts at rest on the first floor of a building and stops at the top floor. The elevator then returns to the first floor. A person stands in the elevator, holding an object (o) hanging from a spring scale. Draw force diagram for the object in the following cases: (A) Elevator hangs at rest at the first floor. (not required to solve here; see lecture video) (B) The elevator starts moving upwards going faster and faster. (not required to solve here; see lecture video) (C) The elevator moves upward with a constant speed. (not required to solve here; see lecture video) (D) The elevator slows down as it approaches the top floor. (E) The elevator starts moving downwards going faster and faster. (F) The elevator moves downwards with a constant speed. (G) The elevator slows down as it approaches the first floor and comes to a stop.

          2] An elevator starts at rest on the first floor of a building and stops at the top floor. The elevator then returns to the first floor. A person stands in the elevator, holding an object (o) hanging from a spring scale. Draw force diagram for the object in the following cases:

(A) Elevator hangs at rest at the first floor. (not required to solve here; see lecture video)

(B) The elevator starts moving upwards going faster and faster. (not required to solve here; see lecture video)

(C) The elevator moves upward with a constant speed. (not required to solve here; see lecture video)

(D) The elevator slows down as it approaches the top floor.

(E) The elevator starts moving downwards going faster and faster.

(F) The elevator moves downwards with a constant speed.

(G) The elevator slows down as it approaches the first floor and comes to a stop.

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2] An elevator starts at rest on the first floor of a building and stops at the top floor. The elevator then returns to the first floor. A person stands in the elevator, holding an object (o) hanging from a spring scale. Draw force diagram for the object in the following cases:

(A) Elevator hangs at rest at the first floor. (not required to solve here; see lecture video)

(B) The elevator starts moving upwards going faster and faster. (not required to solve here; see lecture video)

(C) The elevator moves upward with a constant speed. (not required to solve here; see lecture video)

(D) The elevator slows down as it approaches the top floor.

(E) The elevator starts moving downwards going faster and faster.

(F) The elevator moves downwards with a constant speed.

(G) The elevator slows down as it approaches the first floor and comes to a stop.

Added by Kevin M.

University Physics with Modern Physics

Hugh D. Young 14th Edition

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Solved by Expert Timothy James

09/23/2022

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2] An elevator starts at rest on the first floor of a building and stops at the top floor. The elevator then returns to the first floor. A person stands in the elevator, holding an object (o) hanging from a spring scale. Draw force diagram for the object in the following cases: (A) Elevator hangs at rest at the first floor. (not required to solve here; see lecture video) (B) The elevator starts moving upwards going faster and faster. (not required to solve here; see lecture video) (C) The elevator moves upward with a constant speed. (not required to solve here; see lecture video) (D) The elevator slows down as it approaches the top floor. (E) The elevator starts moving downwards going faster and faster. (F) The elevator moves downwards with a constant speed. (G) The elevator slows down as it approaches the first floor and comes to a stop.

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Transcript

00:01 All right, so let's draw a force diagram for the case that a person stands in an elevator, and the elevator hangs at rest on the first floor.

00:09 So if we draw the person, what we're going to have is just their weight going down, and then the normal force from the floor of the elevator going upwards.

00:22 And they're holding an object from a spring scale.

00:26 So basically what's going to happen is if we look at the object itself, you'll have the restoring force going upwards, the spring force going upwards, and then mg downwards.

00:38 Then part b, we have the elevator starts moving upwards, going faster and faster.

00:43 So now there's an upwards acceleration.

00:45 So if we look at our object, you're going to have your spring force upwards and also the net force is upwards.

00:53 And this is going to be downwards.

00:55 Mg is downwards.

00:57 So we have our spring force going up, and the net force is all.

01:01 Also up because that's the direction of acceleration.

01:04 Part c, the elevator is moving upwards with a constant speed.

01:11 So this will look the same as part a because there's no net force anymore.

01:16 When it's moving at a constant speed, there's no net force.

01:19 D, the elevator slows down as it approaches the top floor.

01:22 So now your spring force is still going upwards...

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