# Kinetic Energy&Work

1. Dec 29, 2013

### harelori

1. The problem statement, all variables and given/known data
*The experiments drawing is attached.
m=0.1kg
Ek at point O (the moment the ball is being pushed) = 1.25 J
D (0 ; 0) , C (0 ; 0.05), E (0.25 ; 0), F (0.50 ; 0), G (0.75 ; 0)
Friction is neglected

1.Complete the chart by typing if the value of each variable is rising / decreasing / constant / equals to zero. (attachment added)
2.Calculate the balls speed at point O.
3.Calculate the work of ∑F that has been working on the ball from A to C. ( W∑F )
4.The ball reaches one of the holes G/F/E - calculate which one it reaches.
5.Add Cartesian axis on the drawing, locate in it the points :C,D,E,F,G and add to the drawing the route of the ball from point C until the point he touches the ground.
6.Players has springs that pushes the spring with a constant F that is higher/lower than the original spring. Which one does one has to use for the ball to fall after point G? (The distance of AA' stays the same)

*I'm having difficulties with basically everything*

2. Relevant equations
Ek=mv^2/2
W=Fx*cosα
W∑F=ΔEk
1/2kΔx^2
W=-ΔU
U=mgh

3. The attempt at a solution

1. At point A'O: v:rising , a:rising, ∑F:constant, Mechanic Energy: rising
At point OC: v:constant , a:0, ∑F:constant, Mechanic Energy: constant.
From point C until the ball touches the ground: v:constant, a:rising, ∑F:rising, Mechanic Energy: constant.

2.
Ek=mv^2/2 => 1.25 = 0.1v^2/2 => 2.5= 0.1v^2 => v=5 m/s

*If the question has anything missing - please write the answer you would have done just without placing the number in the variable. As in a parametric answer.

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Last edited: Dec 29, 2013
2. Dec 29, 2013

### haruspex

Seems to me there is some verbal description of the experiment missing at the start.
Are we to ignore rolling/spin?
As the spring expands from AA' to AO, is the force in the spring increasing, decreasing, or staying the same?
In the chart, which energy does E refer to? Is it just the energy in the ball (PE+KE) or the energy of the whole system, or something else?
You have calculated the velocity of the ball at O (assuming not rolling). What will be the speed at C? What dynamical equations do you know for the flight of the ball after C?

3. Dec 29, 2013

### harelori

We are to ignore the rolling/spinning.
We assume that while the spring expands the force is staying the same.
In the chart, E refers to Mechanic Energy (Ep+Ek).
The speed at C should be 5 m/s,
and the afterwards I suppose it's to be projectile motion

4. Dec 29, 2013

### haruspex

You're told that? Please post all the text describing the experiment.
Yes, but just of the ball or of the whole system (i.e. including the spring)?
Yes.

5. Dec 29, 2013

### harelori

The whole system I suppose, you think you can you help me solve it?