His Kinetic Energy to Kinetic energy of the snow?

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I was watching a video and it showed a man going up a hill through a lift. The engine did work on him so he could gain height/GPE energy. Once he got up there they portrayed two scenarios. In the first one he went down like a normal skier.

In the second example, he simply jumped off the cliff and as he lost height, he gained speed and therefore gained KE and when he got to the ground they said the energy was not destroyed, it is used to do work to dig him into the snow. Now, he doesn’t dig himself down forever, he eventually stops. I wanted to know whether he stopped digging down simply because all Kinetic Energy was used doing work (e.g: He had 1000J energy right before he hit the snow and moved 10 m down, he exerted a force of 100 J) but we have to factor in friction doing work against him right? And also, what kind of energy is he transferring? His Kinetic Energy to Kinetic energy of the snow? And the snow stops moving when he stops moving: That’s because of friction too? Basically I'm confused how the skier uses his Kinetic Energy to do work in this scenario.

Thanks
 

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When he lands, the KE is transferred to another form. In this case, heat.

If he has 1000J of kinetic energy on landing, all 1000J are transferred to other forms once stopped. If not, he is still moving.

If you consider the bottom of the hill to be the 0 GPE point, on landing he will have 0 GPE and 0 KE. Which means the energy has gone elsewhere. In this case, it has been transferred to heat through friction with the snow.

To make it easier to understand, consider me stood on a hill. I have 100J of GPE. I jump, that GPE is converted to KE so at the bottom I have 100J of KE. On landing I transfer that KE to heat energy. If you felt the ground it would be ever so slightly warmer because of this.
 
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Ah ok, got it, thanks! :biggrin:

And just one more thing: For example, if I kicked a ball upwards, I would be doing work on it, granting it KE energy. It starts to gain height. Is it using the Kinetic Energy to do work against the force of gravity? Or also, in a Pendulum, when it is at its lowest height it goes up because it uses its KE energy to do work against gravity?

Thanks.
 
  • #4
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Ah ok, got it, thanks! :biggrin:

And just one more thing: For example, if I kicked a ball upwards, I would be doing work on it, granting it KE energy. It starts to gain height. Is it using the Kinetic Energy to do work against the force of gravity? Or also, in a Pendulum, when it is at its lowest height it goes up because it uses its KE energy to do work against gravity?

Thanks.
The ball and pendulum:

When you swing the pendulum / kick the ball, you give them a certain amount of KE. It is this energy which does work against gravity.

As they go from the bottom to the maximum height, they have KE. When they reach the top (and stop) they have 0 KE and max GPE. As it starts to descend it loses GPE and gains KE.

The pendulum has maximum KE and minimum GPE at the bottom of its swing and maximum GPE and minimum KE at the top. The pendulum loses energy through mechanical friction, this transfers the KE to heat energy as it moves - eventually stopping it swinging. Note that no energy is lost at the point of 0 KE and max GPE - there is no friction.

This applies to the ball also, but with the ball, once it descends it impacts the floor. At this point the KE becomes heat energy.
 

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