Physics Help Forum Ball on inclined plan frictionless
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 Feb 26th 2017, 12:50 PM #1 Junior Member   Join Date: Feb 2017 Posts: 2 Ball on inclined plan frictionless Hi there, I need help for this question. I assumed d=20 and m=2 since i cannot use conservation of energy i couldnt solve it. I found the acceleration which is mgsin30=4.9 i put it on the formula v (final velocity)=u(initial)+at^2 v=4.9t^2 when i put this on the formula s=(u+v/2)*t I got v=14 is that correct ? I could find h and i need help for d and e ( i did not understand since I'm not a native english speaker)
Feb 26th 2017, 05:55 PM   #2
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 Originally Posted by sagnaq997 Hi there, I need help for this question. I assumed d=20 and m=2 since i cannot use conservation of energy i couldnt solve it. I found the acceleration which is mgsin30=4.9 i put it on the formula v (final velocity)=u(initial)+at^2 v=4.9t^2 when i put this on the formula s=(u+v/2)*t I got v=14 is that correct ? I could find h and i need help for d and e ( i did not understand since I'm not a native english speaker)
m = 2 kg, d = 20 m

(I presume you made a force diagram.)

b) Use the definition of sine: $\displaystyle sin(30) = \frac{h}{d}$. So you can find h from here.

c) Your tactic of using Newton's 2nd to find the acceleration is good. But it's $\displaystyle F_{down} = ma = m \cdot (-g~cos(30) )$. You have an extra m in your equation. Now you can finish off with your equation to find v.

d) The ball is now initially traveling up the incline with a new acceleration (deceleration, really) with an initial speed you found in c).

e) In the first part h is the height where the ball started. You need to use the speed in (d) as the initial speed.

Is that detailed enough or do you need more help in understanding what d) and e) are asking for?

-Dan
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Feb 27th 2017, 01:51 AM   #3
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 Originally Posted by topsquark m = 2 kg, d = 20 m (I presume you made a force diagram.) b) Use the definition of sine: $\displaystyle sin(30) = \frac{h}{d}$. So you can find h from here. c) Your tactic of using Newton's 2nd to find the acceleration is good. But it's $\displaystyle F_{down} = ma = m \cdot (-g~cos(30) )$. You have an extra m in your equation. Now you can finish off with your equation to find v. d) The ball is now initially traveling up the incline with a new acceleration (deceleration, really) with an initial speed you found in c). e) In the first part h is the height where the ball started. You need to use the speed in (d) as the initial speed. Is that detailed enough or do you need more help in understanding what d) and e) are asking for? -Dan
hi I did not get the c where does cos come from isn't it sin ?

Feb 27th 2017, 02:37 PM   #4
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 Originally Posted by sagnaq997 hi I did not get the c where does cos come from isn't it sin ?
Yes it should be mg sin(30). Thanks for the catch.

-Dan
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 Tags ball, frictionless, inclined, plan

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