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# Energy transfers(kinetic energy) but involves height watch

1. A ball with 10J of kinetic energy is thrown so that it lands on a roof travelling horizontally with 4J of kinetic energy.

If the ball has a mass of 0.23 kg, what is the height of the roof , measured from the point of release?
Picture:

Any hints i.e. 2 equations etc
Attached Images

2. (Original post by Nirm)
A ball with 10J of kinetic energy is thrown so that it lands on a roof travelling horizontally with 4J of kinetic energy.

If the ball has a mass of 0.23 kg, what is the height of the roof , measured from the point of release?

Any hints i.e. 2 equations etc
There is not enough information given to produce an answer. It's rather poorly phrased and ambiguous at best.

For a start, there is no information given regarding the direction of the throw, whether the ball is thrown from a moving or stationary platform, etc. etc.

Is this part of a multi-part question?

You need to post the full question including any diagrams.
3. (Original post by uberteknik)
There is not enough information given to produce an answer. It's rather poorly phrased and ambiguous at best.

For a start, there is no information given regarding the direction of the throw, whether the ball is thrown from a moving or stationary platform, etc. etc.

Is this part of a multi-part question?

You need to post the full question including any diagrams.
Attached Images

4. (Original post by Nirm)
You need to state the angle the ball is thrown at.
5. (Original post by uberteknik)
You need to state the angle the ball is thrown at.
Question doesnt state it. The picture i gave was from the question itself. Does that mean there is too little information?
6. (Original post by Nirm)
A ball with 10J of kinetic energy is thrown so that it lands on a roof travelling horizontally with 4J of kinetic energy.

If the ball has a mass of 0.23 kg, what is the height of the roof , measured from the point of release?
Picture:

Any hints i.e. 2 equations etc
The other comments are wrong. You have all the information you need.

The ball has 10J of kinetic energy, and when it lands it has 4J of kinetic energy. Assuming no air resistance, the remaining 6J of energy must have been transferred into gravitational potential energy.

Remember that E = mgh, where E is the change in gravitational potential energy, m is mass of the object, and h is the change in height.

Hope this helps :-)

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7. (Original post by uberteknik)
You need to state the angle the ball is thrown at.
I'm going to go ahead and disagree that you need the angle. The only energy transfer in this question (assuming no resistive forces) is kinetic to gpe. Hence if the ball loses 6J of Ke then that must have been stored in the field as gpe, hence the change in gpe is 6J, regardless of the angle thrown. Energy isn't a vector, so if the ball had 10J of Ke at the start, it doesn't matter if this was largely due to vertical or horizontal motion, if it loses 6J, that 6J must have gone somewhere; it was stored in the field due to conservation of energy.
8. (Original post by ExcitinglyMundane)
The other comments are wrong. You have all the information you need.

The ball has 10J of kinetic energy, and when it lands it has 4J of kinetic energy. Assuming no air resistance, the remaining 6J of energy must have been transferred into gravitational potential energy.

Remember that E = mgh, where E is the change in gravitational potential energy, m is mass of the object, and h is the change in height.

Hope this helps :-)

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Have no idea why i didn't think like you did . Thank you so much, got the right answer
9. (Original post by Protoxylic)
I'm going to go ahead and disagree that you need the angle. The only energy transfer in this question (assuming no resistive forces) is kinetic to gpe. Hence if the ball loses 6J of Ke then that must have been stored in the field as gpe, hence the change in gpe is 6J, regardless of the angle thrown. Energy isn't a vector, so if the ball had 10J of Ke at the start, it doesn't matter if this was largely due to vertical or horizontal motion, if it loses 6J, that 6J must have gone somewhere; it was stored in the field due to conservation of energy.
For some reason I fixated on velocity.

You are of course, correct.

It's late. Time for bed methinks.
10. (Original post by Nirm)
Have no idea why i didn't think like you did . Thank you so much, got the right answer
Haha, it just comes with practice! :-D

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11. (Original post by ExcitinglyMundane)
Haha, it just comes with practice! :-D

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AS physics is so much more confusing than GCSE . But it gets interesting at A2 from what i have heard.
12. (Original post by Nirm)
AS physics is so much more confusing than GCSE . But it gets interesting at A2 from what i have heard.
I found them equally as interesting, but A2 was definitely a little harder. If you need any other help, feel to drop me a pm. I can't guarantee a quick answer, but I'm happy to help :-)

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13. (Original post by uberteknik)
For some reason I fixated on velocity.

You are of course, correct.

It's late. Time for bed methinks.
When you mentioned it, I too started to think down that road haha.
14. You may have already calculated the answer however, another way of doing this is to calculate the speed at 10J and 4J by re arranging KE=0.5mv2 . Then assuming acceleration due to gravity = 9.81ms-2. You can re-arrange equation v2 = u2+ 2as to make s (displacement) the subject and sub in the values.
15. (Original post by MSB47)
You may have already calculated the answer however, another way of doing this is to calculate the speed at 10J and 4J by re arranging KE=0.5mv2 . Then assuming acceleration due to gravity = 9.81ms-2. You can re-arrange equation v2 = u2+ 2as to make s (displacement) the subject and sub in the values.
This would work, but is significantly more complex. Although it would help practice other techniques, it is better to practice finding the optimum way to tackle a problem.
16. Thank you for all the replies guys

(Original post by ExcitinglyMundane)
I found them equally as interesting, but A2 was definitely a little harder. If you need any other help, feel to drop me a pm. I can't guarantee a quick answer, but I'm happy to help :-)

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Thanks
(Original post by MSB47)
You may have already calculated the answer however, another way of doing this is to calculate the speed at 10J and 4J by re arranging KE=0.5mv2 . Then assuming acceleration due to gravity = 9.81ms-2. You can re-arrange equation v2 = u2+ 2as to make s (displacement) the subject and sub in the values.
Interesting but definitely the harder method but thank you for the insight.

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