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    serenitymantra's Avatar
    serenitymantra Posts: 28, Reputation: 1
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    #1

    Sep 22, 2008, 01:08 PM
    Velocity on an Incline
    Suppose you begin sliding down a 15 degree ski slope. Ignoring air resistance, how fast will you be moving after 10s?

    I need help setting it up. Any guidance will be appreciated. Thanks!
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Sep 22, 2008, 01:12 PM

    Remember that F=ma. Here F is the force of gravity along a 15 degree incline. If you resolve the force of gravity into components along the slope and perpendicular to the slope, you should be able to see that here F = mg sin(15 deg). So now you can determine its acceleration a. The next step is to apply the equation of motion for a body under constant acceleration to find its velocity at t=10 sec.
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    serenitymantra Posts: 28, Reputation: 1
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    #3

    Sep 22, 2008, 01:20 PM
    Quote Originally Posted by ebaines View Post
    Remember that F=ma. Here F is the force of gravity along a 15 degree incline. If you resolve the force of gravity into components along the slope and perpendicular to the slope, you should be able to see that here F = mg sin(15 deg). So now you can determine its acceleration a. The next step is to apply the equation of motion for a body under constant acceleration to find its velocity at t=10 sec.
    Ma? Mg?
    ballengerb1's Avatar
    ballengerb1 Posts: 27,378, Reputation: 2280
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    #4

    Sep 22, 2008, 01:23 PM
    Do you want an answer that also ignores friction as well as air resistance?
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    ebaines Posts: 12,131, Reputation: 1307
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    #5

    Sep 22, 2008, 01:26 PM
    Quote Originally Posted by serenitymantra View Post
    ma? mg?
    Oh boy. Given the data you've provided the only way to do this problem is to start with an understanding of Newtons' 3rd Law:

    F = ma, or Force = mass time acceleration.

    Does this sound familiar? If not, then you'd better go back and read your text book.
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    #6

    Sep 22, 2008, 02:28 PM
    Quote Originally Posted by ballengerb1 View Post
    Do you want an answer that also ignores friction as well as air resistance?
    Yes, ignoring both friction and air resistance.
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    serenitymantra Posts: 28, Reputation: 1
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    #7

    Sep 22, 2008, 02:29 PM
    Quote Originally Posted by ebaines View Post
    Oh boy. Given the data you've provided the only way to do this problem is to start with an understanding of Newtons' 3rd Law:

    F = ma, or Force = mass time acceleration.

    Does this sound familiar? If not, then you'd better go back and read your text book.
    We never talked about force. This is the guy's 1st time teaching, so he's going pretty fast and everyone in this class is lost.
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    ballengerb1 Posts: 27,378, Reputation: 2280
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    #8

    Sep 22, 2008, 02:32 PM
    He is going fast likely out of fear. Ask/tell him to slow down and try to give more examples and visuals. I supervise first year science teachers who graduate from our university with a type 25 teaching certificate. Its very common for them to go too fast, ask for more examples.
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    ebaines Posts: 12,131, Reputation: 1307
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    #9

    Sep 22, 2008, 02:33 PM

    I suppose you can ignore force if you simply assume that the acceleration along the slope is a = g sin(15 degrees). Here g is the acceleration due to gravity, or 9.8 m/s^2. From this you can determine the velocity after 10 seconds.
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    serenitymantra Posts: 28, Reputation: 1
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    #10

    Sep 22, 2008, 03:07 PM
    Quote Originally Posted by ballengerb1 View Post
    He is going fast likely out of fear. Ask/tell him to slow down and try to give more examples and visuals. I supervise first year science teachers who graduate from our university with a type 25 teaching certificate. Its very common for them to go too fast, ask for more examples.
    We try. He just looks at us and say.. it's easy guys.. it's not that difficult. I told him I wanted some tutoring from the lab, his response is that 'don't try to hard.'
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    serenitymantra Posts: 28, Reputation: 1
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    #11

    Sep 22, 2008, 03:17 PM
    Quote Originally Posted by ebaines View Post
    I suppose you can ignore force if you simply assume that the acceleration along the slope is a = g sin(15 degrees). Here g is the acceleration due to gravity, or 9.8 m/s^2. From this you can determine the velocity after 10 seconds.
    I did that initially, but I wasn't sure I was on the right track. I ended up with 25.4 m/s.
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    ballengerb1 Posts: 27,378, Reputation: 2280
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    #12

    Sep 22, 2008, 05:00 PM
    Half of us graduated in the top half of our class, the rest did not.
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #13

    Sep 23, 2008, 05:29 AM
    Quote Originally Posted by serenitymantra View Post
    I did that initially, but I wasn't sure I was on the right track. I ended up with 25.4 m/s.
    You got it - 25.4 m/s is correct.
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    babybean_06 Posts: 1, Reputation: 1
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    #14

    Feb 2, 2009, 11:10 AM
    Quote Originally Posted by serenitymantra View Post
    Suppose you begin sliding down a 15 degree ski slope. Ignoring air resistance, how fast will you be moving after 10s?

    I need help setting it up. Any guidance will be appreciated. Thanks!
    7m
    brat269's Avatar
    brat269 Posts: 1, Reputation: 1
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    #15

    Oct 13, 2009, 12:00 AM

    9.8m/s*sin(15) *10
    25m/s
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    gertkip Posts: 1, Reputation: 1
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    #16

    Feb 11, 2012, 10:29 AM
    a=+gsin theta
    a=9.8(sin 15)
    a=2.54m/s^2
    however a= change in velocity/time
    velocity=a*time
    2.54*10= 25.4m/s

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