Falling Man Lands: Distance from Building?

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In summary, the problem presents a man sliding off a roof at a 45 degree angle, with negligible friction and air resistance. He slides 4m down the roof, falls off, and lands a certain distance away from the building. Another man stands 4m away from the building and is 1.2m tall. The main goal is to find the distance the falling man lands from the building and if he hits the man below. To solve this problem, the two phases of the motion must be identified - the first being the slide down the roof and the second being the fall off the roof. The initial velocity of the falling man can be calculated by finding the horizontal component of the roof's angle and using that in conjunction with
  • #1
quicksilver123
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Homework Statement


a man slides off a roof that makes an angle of 45 degrees below the horizontal. friction and air resistance neglig. he slides 4m, falls off and lands a certain distance away from the building. another man stands 4m away and is 1.2m tall. how far from the building does the falling man land and does he hit the man below?

Homework Equations



i don't really know what to do here.

The Attempt at a Solution



all I've done so far is found the horizontal component (u) of the roof he fell off of. i don't even think that this is relevant.
cos45=u/4m
u=2(sqrt2)
guidence?
 
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  • #2
In general, we can help you solve problems where you are stuck. But, we can't really teach you the physics from the beginning. If you really have no idea, then you should backtrack and try some easier problems.

What physics do you know?

The man's motion has two phases here, can you identify them?
 
  • #3
Right... I do know some physics but just need some help with the question...
Obviously there is an x-component to the slide down the roof, which is a gravity component... if you could help me find that it would be great.

the slide down the roof being the first part of the motion and the falling off the roof being the second.
 
  • #4
quicksilver123 said:
Right... I do know some physics but just need some help with the question...
Obviously there is an x-component to the slide down the roof, which is a gravity component... if you could help me find that it would be great.

the slide down the roof being the first part of the motion and the falling off the roof being the second.

What do you know about sliding down a roof?
 
  • #5
uhm... not much?

listen man, I'm guessing that there's an x-component to the gravity that causes continued x-axis momentum/velocity after the man leaves the roof; otherwise it would just be a vertical fall. now if you can help me figure out how to get that x-component, without knowing an initial velocity... i would be grateful.
and then maybe a tip on getting the correct answer for the second phase of the question.
 
  • #6
Do you know the term "incline" or "inclined plane"?

Have you heard of the term "vector"?

What about Kinetic and Potential energy?
 
  • #7
quicksilver123 said:
i'm guessing that there's an x-component to the gravity
No need to guess. There isn't.

[edit] to be a bit more helpful: the advice is to make a drawing, not wait until someone does it for you
 
Last edited:
  • #8
BvU said:
No need to guess. There isn't.

[edit] to be a bit more helpful: the advice is to make a drawing, not wait until someone does it for you
Honestly, I don't understand. Without an x component to the velocity in the first part of the question, wouldn't the object just fall vertically once it exits the roof? Obviously there is some form of horizontal momentum.
That's the first thing I did... bit rude.
 
  • #9
quicksilver123 said:
Without an x component to the velocity in the first part of the question, wouldn't the object just fall vertically once it exits the roof?
Yes, you are right that there is an x component (and a y component) of the velocity, and if there wasn't an x component, yes it would just fall vertically. But what you originally said was:
quicksilver123 said:
i'm guessing that there's an x-component to the gravity
There is no x component to gravity.

So did you calculate the x and y components of the velocity just as he is falling off of the roof?

Edit: Was there a height of the roof given, or did I just miss it?
 
  • #10
TomHart said:
Yes, you are right that there is an x component (and a y component) of the velocity, and if there wasn't an x component, yes it would just fall vertically. But what you originally said was:

There is no x component to gravity.

So did you calculate the x and y components of the velocity just as he is falling off of the roof?

Edit: Was there a height of the roof given, or did I just miss it?

Yeah the height of the roof was given.. sorry its been a long night.
The height of the roof is given as 9m.

I remember doing FBD diagrams where an object was sliding down an incline, and I recall that there was an x-component to the forces when gravity was the only actor. I suppose I should review that.
 
  • #11
It was probably a bad answer on my part to say there is no x component of gravity because it all depends on how you define your axes.

Edit: I guess I tend to think as the y-axis being vertical and x-axis being horizontal, but that certainly is not always the case. And as a matter of fact, for the first part of the problem (sliding down the roof), it seems to make more sense to NOT define the axes as vertical and horizontal. I would define the +x axis to be in the direction of the downward slope of the roof.
 
  • #12
Thanks.
 
  • #13
quicksilver123 said:
listen man, I'm guessing that there's an x-component to the gravity
OK, we've dealt with that. Now what about a little sketch of what's happening ?
quicksilver123 said:
he slides 4m, falls off and lands a certain distance away from the building
Not so hard, or is it ? We do get another bit of input in post #10, but I still have a little something missing to draw the picture for you !
Is the 9 m the top of the roof ? Where does the 4 m start ?

upload_2017-1-13_0-15-59.png
 

1. How far can a person fall from a building and survive?

The survival rate of falling from a building depends on various factors such as the height of the building, the surface of the landing, and the position of the person upon impact. Generally, a fall from a height of more than 10 stories (approximately 100 feet or 30 meters) is considered lethal, but there have been rare cases of people surviving falls from much greater heights.

2. What is the average distance a person falls after jumping from a building?

The average distance a person falls when jumping from a building depends on the height of the building and the individual's body position during the fall. On average, a person will fall approximately 1,200 feet (365 meters) in 12 seconds from a building that is 100 stories high. However, this distance can vary greatly depending on the specific circumstances of the fall.

3. How does air resistance affect a falling person's distance from a building?

Air resistance, also known as drag, is a force that opposes the motion of a falling object. As a person falls from a building, they will experience increasing air resistance, which will eventually balance out the force of gravity. This means that the person will eventually reach a constant terminal velocity where their rate of falling will not increase any further. Therefore, the distance a person falls from a building will depend on their terminal velocity, which in turn is affected by their body position and the surface area of their body.

4. Can a person control their distance from a building while falling?

Although a person cannot control their terminal velocity, they can control their body position to some extent to increase or decrease their air resistance. By spreading out their body, they can increase their surface area and thus increase their air resistance, causing them to fall at a slower speed. On the other hand, by making themselves more streamlined, they can decrease their air resistance and fall faster. However, these adjustments will only have a minor impact on the distance the person falls from the building.

5. How does the surface of the landing affect the distance a person falls from a building?

The surface of the landing can greatly affect the distance a person falls from a building. A softer surface, such as a pile of snow or a bush, will provide more cushioning and decrease the impact force, resulting in a shorter distance fallen. On the other hand, a hard surface, such as concrete, will provide less cushioning and increase the impact force, resulting in a greater distance fallen. This is why it is crucial for individuals to aim for a softer surface when attempting to survive a fall from a building.

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