# Ball on inclined plan frictionless

#### 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)

#### topsquark

Forum Staff

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

#### sagnaq997

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 ?

1 person

#### topsquark

Forum Staff
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