Physics: Post your doubts here!

[princess Anu]

Distance XZ is constant.
If speed is high then XZ is covered quickly so t is less.
If speed is low (after rebound inelastic) XZ is covered in more time.

You must also compare area under vt graph. XZ is constant so area must remain constant.

XY isn't constant,no? because the question says it comes to rest somewhere between XY so we don't exactly know if it returns to its initial position?

 

[DaniyalK]

but the ans is C
its nov 2013 p11

Final is half of the initial, so half of the kinetic energy is lost... Ek/2

 

[BhaiArshad]

XY isn't constant,no? because the question says it comes to rest somewhere between XY so we don't exactly know if it returns to its initial position?

Sorry. Read All XZ as YZ. I was talking about the Flat area.

Distance YZ is constant.
If speed is high then YZ is covered quickly so t is less.
If speed is low (after rebound inelastic) YZ is covered in more time.

You must also compare area under vt graph. YZ is constant so area must remain constant.

 

[princess Anu]

Yes, its the net work done

The net work done should be the area between the unloading and loading line ,no?

 

[eliyeap]

\
how B?

E= stress/strain= F/A/x/l
E=Fl/xA
E=Fl/ delta l (l^2)
E and F are both constant, so B

 

[eliyeap]

The net work done should be the area between the unloading and loading line ,no?

The area between is the thermal energy dissipated. For a rubber, when it is extended they say that there is no permanent extension, however there will be heat exerted. The shaded area is the net work done and the area under the graph is the work recovered

 

[eliyeap]

View attachment 54937

P= 1000*(30/100)*9.81

 

[princess Anu]

Sorry. Read All XZ as YZ. I was talking about the Flat area.

Distance YZ is constant.
If speed is high then YZ is covered quickly so t is less.
If speed is low (after rebound inelastic) YZ is covered in more time.

You must also compare area under vt graph. YZ is constant so area must remain constant.

you mean the shaded areas should be equal , right?

 

[princess Anu]

The area between is the thermal energy dissipated. For a rubber, when it is extended they say that there is no permanent extension, however there will be heat exerted. The shaded area is the net work done and the area under the graph is the work recovered

Sorry but I don't get you.. can u shade for me the respective areas please

 

[princess Anu]

help

 

[BhaiArshad]

you mean the shaded areas should be equal , right?

Yes as that represents the distance YZ. If area changes then we have actually changed YZ which cannot happen.

 

[eliyeap]

Sorry but I don't get you.. can u shade for me the respective areas please

The work recovered+ work not recovered= net work done

 

[nehaoscar]

How and why D?

 

[nehaoscar]

Why will the line NOT be part of a circle?

 

[eliyeap]

How and why D?

The question is asking for Power. The first 2 answers give KE which is wrong. Its is D because you have to take into account the diff in mass. C just considers M1.

 

[ashcull14]

why doesnt g change

 

[DaniyalK]

helpView attachment 54939

Volume = 2000 * 10 = 20000
Mass = 20000 * 1.3 = 26000
KE = 0.5 * 26000 * 10^2 = 1300J
efficiency is 50% so answer is 650KW

Why will the line NOT be part of a circle?

It is projectile motion, so the path is parabolic.

 

[DaniyalK]

View attachment 54941
why doesnt g change

Because gravitational field strength hasn't changed.

 

[a_wiserME!!]

Can someone please explain. This question pls

 

[nehaoscar]

The question is asking for Power. The first 2 answers give KE which is wrong. Its is D because you have to take into account the diff in mass. C just considers M1.

But then why do you need to consider the difference in mass? Won't you add the masses to get the total power? :S