b----g4
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Hi, I'm stuck on this Physics A Level Question and am wondering if anyone can help me...

Figure 1 shows a spacecraft of total mass 610kg entering the atmosphere at a speed of 5.5kms-1.
....
As the parachute-spacecraft system decelerates, it falls through a vertical distance of 49m and loses 2.2 x 10^5 J of kinetic energy.
During this time, 3.3 x 10^5 J of energy is transferred from the system to the atmosphere. The total mass of the system is 610kg.
Calculate the acceleration due to gravity as it falls through this distance.

Any help would be greatly appreciated Thank you for reading!
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lordaxil
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From the loss in kinetic energy, you can work out the speed of parachute-spacecraft system after falling 49m, then use the appropriate SUVAT formula to find the average acceleration over that distance. You have to assume that the acceleration is constant (in practice, it will increase slightly).
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b----g4
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(Original post by lordaxil)
From the loss in kinetic energy, you can work out the speed of parachute-spacecraft system after falling 49m, then use the appropriate SUVAT formula to find the average acceleration over that distance. You have to assume that the acceleration is constant (in practice, it will increase slightly).
Ah - sorry, I've spliced together the question parts badly - the initial velocity of 5.5kms-1 doesn't apply to this situation; it's a value from earlier. With that in mind, do you have any other idea as to how to solve this? I'm figuring their value for the loss of energy must have something to do with it, but no clue what...
Thank you very much for the response, my bad for messing up the question!
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lordaxil
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Ah - I see now.

If you use the SUVAT equation, and write down an expression for the change in kinetic energy, you will see that the initial and final velocities will be eliminated, allowing you to work out directly the average force by simply dividing the energy loss by distance falling. This is just equivalent to work done = force x distance.

The problem is how to combine the loss of KE with loss of energy to atmosphere. This is really the crux of the question, and I don't want to spoil it for you, but try to draw a force diagram with air resistance (opposing motion) and weight (opposite to air resistance) and think about which way the resultant force will point. Once you have done that, you should be able to assign the forces calculated from the two energy changes you have been given, and the remaining term is just the weight = mg. Rearrange the expression to get average g.
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b----g4
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(Original post by lordaxil)
Ah - I see now.

If you use the SUVAT equation, and write down an expression for the change in kinetic energy, you will see that the initial and final velocities will be eliminated, allowing you to work out directly the average force by simply dividing the energy loss by distance falling. This is just equivalent to work done = force x distance.

The problem is how to combine the loss of KE with loss of energy to atmosphere. This is really the crux of the question, and I don't want to spoil it for you, but try to draw a force diagram with air resistance (opposing motion) and weight (opposite to air resistance) and think about which way the resultant force will point. Once you have done that, you should be able to assign the forces calculated from the two energy changes you have been given, and the remaining term is just the weight = mg. Rearrange the expression to get average g.
Ahhh, got it. Thank you so much! Drawing out the forces is a new way of looking at those kinds of questions for me - thank you!
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lordaxil
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Great! Force diagrams (or in general, any kind of diagram) can be very useful when trying to work out what's going on.
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Student 999
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Could someone post the working out
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lordaxil
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Why don't you start by posting what you've done so far, and we can see where we can help?
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connorh315
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(Original post by b----g4)
Hi, I'm stuck on this Physics A Level Question and am wondering if anyone can help me...

Figure 1 shows a spacecraft of total mass 610kg entering the atmosphere at a speed of 5.5kms-1.
....
As the parachute-spacecraft system decelerates, it falls through a vertical distance of 49m and loses 2.2 x 10^5 J of kinetic energy.
During this time, 3.3 x 10^5 J of energy is transferred from the system to the atmosphere. The total mass of the system is 610kg.
Calculate the acceleration due to gravity as it falls through this distance.

Any help would be greatly appreciated Thank you for reading!
Would you be able to share these questions? They look quite helpful for my revision and I could do with them if you don't mind. Thanks!
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b----g4
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(Original post by connorh315)
Would you be able to share these questions? They look quite helpful for my revision and I could do with them if you don't mind. Thanks!
Hi, I'm really sorry, I can't find this exact sheet. But there's a chance it came from the Umutech website, which I'd recommend anyways - it's very useful and has lots of past questions sorted by topic. Sorry about that!
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mojin
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(Original post by b----g4)
Ahhh, got it. Thank you so much! Drawing out the forces is a new way of looking at those kinds of questions for me - thank you!
hi there I am doing this question now and I have done Ep = mgh. and have rearranged it to Ep/mh = g. So i've gotten 330000-220000/610x49=3.7m/s^-2 to 2sf. Did you get an answer similar to this? or at least would you know if this makes sense and is right?
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