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# Working out the energy watch

1. In this questions it says 'A mass of 1kg hangs at the end of a string. It is drawn to one side so that it rises through 0.1m. A length of glass tubing is fixed so that when the 1kg mass is released it swings back and breaks the tubing. After breaking the glass it continues to swing upwards on the other side, but only until it rises through 0.06m. How much energy was needed to break the glass?
Any ideas on how to tackle this question?
2. (Original post by JBKProductions)
In this questions it says 'A mass of 1kg hangs at the end of a string. It is drawn to one side so that it rises through 0.1m. A length of glass tubing is fixed so that when the 1kg mass is released it swings back and breaks the tubing. After breaking the glass it continues to swing upwards on the other side, but only until it rises through 0.06m. How much energy was needed to break the glass?
Any ideas on how to tackle this question?
Work out the potential energy at 0.1 m (mgh) Then at 0.06 m. Take g = 9.81 m s^-2.

work out the difference between the two, hence you have the energy needed to break the glass, as energy is always conserved.

Hope that helps you

Spoiler:
Show
0.392 J (to 3 sig. figs.)
3. (Original post by callum Honisett)
Work out the potential energy at 0.1 m (mgh) Then at 0.06 m. Take g = 9.81 m s^-2.

work out the difference between the two, hence you have the energy needed to break the glass, as energy is always conserved.

Hope that helps you

Spoiler:
Show
0.392 J (to 3 sig. figs.)
Yes i fully understood your explanation thanks
4. (Original post by JBKProductions)
Yes i fully understood your explanation thanks
5. (Original post by callum Honisett)
If you dont mind theres a question telling me to state what power is it developing, if an engine discharges 4000kg of water per minute with a speed of 15ms-1.
Any idea on this one?
Edit: The only thing i can actually work out with this is the kinetic energy
6. (Original post by JBKProductions)
If you dont mind theres a question telling me to state what power is it developing, if an engine discharges 4000kg of water per minute with a speed of 15ms-1.
Any idea on this one?
Edit: The only thing i can actually work out with this is the kinetic energy
The two equations for power are : P = fv or P = fd/t.

I'm just going to try and relate them .
7. Do you know if the water is falling vertically or the acceleration of the water as it is discharged?
8. (Original post by callum Honisett)
Do you know if the water is falling vertically or the acceleration of the water as it is discharged?
doesnt say anything about vertically this is the question word for word 'An engine discharges 4000kg of water per minute with a speed of 15m/s. What power is it developing?'
9. (Original post by JBKProductions)
doesnt say anything about vertically this is the question word for word 'An engine discharges 4000kg of water per minute with a speed of 15m/s. What power is it developing?'
Have you got the answer there, I think it may be 9800 W
10. (Original post by callum Honisett)
Have you got the answer there, I think it may be 9800 W
Sorry i dont have the answer with me my teacher likes to be a ******* and not give us the answers lol but if you dont mind explaining how did you get that answer?
11. (Original post by JBKProductions)
Sorry i dont have the answer with me my teacher likes to be a ******* and not give us the answers lol but if you dont mind explaining how did you get that answer?
Actually sorry , Ignore that answer , I messed the calculation up.

I'm not sure on that one, it seems like there is a missing piece of info.

Is there anything else you need help with. I usually have no probs with these questions.
12. (Original post by callum Honisett)
Actually sorry , Ignore that answer , I messed the calculation up.

I'm not sure on that one, it seems like there is a missing piece of info.

Is there anything else you need help with. I usually have no probs with these questions.
Ok i have one more question (or maybe 2 lol)
A car is moving with a steady speed of 10m/s. Drag forces acting on it total 300N. The engine provides 10000W of power to the car.
(i)Calculate the power output of the car
(ii)Calculate the energy loss per second of the car
(iii)In what form is this energy wasted
13. (i) P = Fv , work out the power 'wasted' in overcoming the resistive force. Then subtract from the 10000 W

(ii) Power is energy per second Work this out for the resistive forces

(iii) Sound energy, heat energy.
14. (Original post by callum Honisett)
(i) P = Fv , work out the power 'wasted' in overcoming the resistive force. Then subtract from the 10000 W

(ii) Power is energy per second Work this out for the resistive forces

(iii) Sound energy, heat energy.
ok for the first one i got 7000W so its the second part just 3000 J s^-1?
15. (Original post by JBKProductions)
ok for the first one i got 7000W so its the second part just 3000 J s^-1?
Just got back , and I think you're correct.

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