Urgent Dynamics Problem Help Needed: 12-101 Hibbler 13th ed.

You know the horizontal distance and the time, so...In summary, the conversation discusses a problem involving a skier leaving a ramp at an angle and determining their initial speed and the speed at which they strike the ground. The equation VA=80/cos15(t) is used to solve for VA, and then the equation Vy=(Vo)y+at is used to find the speed at which the skier strikes the ground, which can be found by calculating the square root of (VBy)^2 + (VBx)^2.
  • #1
AEfly
6
0
The Problem.
12-101 Hibbler dynamics 13th edition.


It is observed that the skier leaves the ramp A at an angle θA=15 degrees with the horizontal. if he strikes the ground at B, deterime his initial speed VA and the speed at which he strikes the ground (at B).

http://s3.amazonaws.com/answer-board-image/d324abb1-8b50-49a3-a0dd-e2375f1be1a4.jpeg (Ignore the values not in the diagram itself)

My issue:
I understand how to get VA but, I have no idea how to the the speed at which he strikes the ground at B. Any help would be very appreciated.

I do not even know where to start to find VB.
 
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  • #2
Hint: How far below A is B?
 
  • #3
64m. I just don't know how to set up and re work the equations to solve for VB. I understand for VA its

80=VA(cos15)t

-64=VA(sin15)t-(1/2)(9.81)t^2

where I would sub in VA=80/cos15(t) to solve for t and then plug t back into the first equation.
 
  • #4
AEfly said:
64m. I just don't know how to set up and re work the equations to solve for VB. I understand for VA its

80=VA(cos15)t

-64=VA(sin15)t-(1/2)(9.81)t^2

where I would sub in VA=80/cos15(t) to solve for t and then plug t back into the first equation.
Since you know VA, you can use either equation to solve for t. (Use the first one, of course.)

How does Vy depend on time?

(There are several ways to get the answer; one way just uses the distance, but since you have the time why not use it.)
 
  • #5
I know VA and t just not how to get VB. Doesnt Vy increase with time in this case as gravity acts downward?
 
  • #6
AEfly said:
Doesnt Vy increase with time in this case as gravity acts downward?
Right. What's the kinematic equation describing that relationship?
 
  • #7
Vy=(Vo)y+at ?
 
  • #8
AEfly said:
Vy=(Vo)y+at ?
Sure.
 
  • #9
But how does VB relate into that? I am guessing I need to find VBy and VBx and then do the

sqrt of (VBy)^2 + (VBx)^2
 
  • #10
AEfly said:
But how does VB relate into that? I am guessing I need to find VBy and VBx and then do the

sqrt of (VBy)^2 + (VBx)^2
Exactly. VBx should be trivial.
 

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The "Urgent Dynamics Problem Help Needed: 12-101 Hibbler 13th ed." is about a specific problem related to dynamics, a branch of physics that deals with the motion and forces of objects.

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