Physics: Work. Conservation of energy (4)

[NPulgarin]

If he use h (initial) as "0" the the Final h is "4" ) he is going 4m up, but you can use 7m and 11m..it will give u a proportional answer.

[whiteninjaooo]

at 4:19 where is the 2/5 coming from?and why?

[Oboetoke100]

hows the height 4? lol

[whiteninjaooo]

@Oboetoke100

11m-7m=4m

u need to use 7m not 8m

[sunjz]

@Oboetoke100 11-7=8

[sunjz]

@sunjz 11-7=4* sry

[mohamed140817]

How is the height 4????????

[bchou222]

the girl seems so enthusiastic!!!

[WongeneKIM]

Thank you for your lectures!

[bluejimmy168]

i dont see why i can do this without the mass. Show me please.

[StompTroopa]

@bluejimmy168

It's because in the way that he has set up the equation, where Ui = Kf, then this can be expressed as

mgh = 1/2 mv^2. Solving for V^2 we get V^2 = mgh / 1/2m then as you can see the two "m" terms can be cancelled out leaving just V^2 = gh / 1/2. If you solve the equation then you should get the same answer as if you had included the mass.

[bluejimmy168]

@StompTroopa oh Thank you so much :)

[sugarcanelies]

@bluejimmy168 when you look at the formula both potential energy and kinetic energy have mass. so mgh+0.5mv^2=mgh+0.5mv^2. You would be able to cancel out the mass from the formula since they are all the same, and solve the problem without it.