1,000,000 Question Thread :D

[kenhung123]

Uploaded sorry forgot.

[Aden]

I think you forgot to add the 1.5m that the shot put was launched from:

[kenhung123]

Thank you very much for your help Aden!

[kenhung123]

Work=fx cos theta, where f=ma
If its at constant speed doesn't it mean a=0, thus f=0N
0*90*cos90=0J?

[Akirus]

From what I understand, the net force is equal to 0, which means the crane must exert force equal to the weight of the 800kg load:







Then to calculate work done:

[kenhung123]

So there is acceleration?

[Akirus]

No, because the force of gravity would exert 7840N downwards, which is offset by the force exerted by the crane (which is equal to the force of gravity = 7840N).

i.e.

[kenhung123]

so why is there work done?

[appianway]

Work's expressed as Fd, where F is the force. Therefore if the crane applies a force (needed to keep it in equilibrium so that it doesn't accelerate downwards) and moves through a distance, work is done. This is also seen by looking at the fact that gravitational potential energy is gained as the weight moves up - work must be done to transfer this energy.

[kenhung123]

Thanks

[kenhung123]

I did
Ek=0.5*0.1*4^2
Ek=1/2kx^2=0.2
x^2=0.4
x=0.63m

[Aden]

The spring constant:

Kinetic energy of the ball:

Elastic Potential Energy:


or

[kenhung123]

Thanks,

You know how an isolated system can't exist, why is it sometimes they ask in questions whether momentum is conserved when it never can be?

[Aden]

That is just like asking why we sometimes omit the friction or air resistance force from a question, or why we only analyse the complex motion of an object according to its centre of mass, when there are obviously different parts of that object that undergo different forms and magnitude of motion. =\

[appianway]

Momentum is conserved in the moment of a collision, however, not all momentum may be transferred to the objects in question because the system might not be completely isolated. These effects can often be negligible though.