# As level physics question helpWatch

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Thread starter 3 years ago
#1 How would you solve Q8? Thank you!
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3 years ago
#2
(Original post by Samhil) How would you solve Q8? Thank you!
Think about what would the apparent weight be if the astronaut was in a rocket accelerating upwards at a rate equal to 5g in zero gravity?
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Thread starter 3 years ago
#3
(Original post by Mehrdad jafari)
Think about what would the apparent weight be if the astronaut was in a rocket accelerating upwards at a rate equal to 5g in zero gravity?
Would they not appear to be weightless?

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3 years ago
#4
(Original post by Samhil)
Would they not appear to be weightless?

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It depends. They would appear to be weightless if the rocket wasn't accelerating in the absence of gravitational fields (which is fairly intuitive). But the question assumes not only that the rocket is in a gravitational field, but also that it's taking of (accelerating upwards) from the surface of the earth.

samhill: Post edited
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Thread starter 3 years ago
#5
(Original post by Mehrdad jafari)
It depends. They would appear to be weightless if the rocket wasn't accelerating in the absence of gravitational fields (which is fairly intuitive). But the question assumes that the rocket is taking of (accelerating upwards) from the surface of the earth.
Ah right! So as the rocket is accelerating, then the weight force of the astronaut decreases because the gravitational pull from the earth gets weaker? I'm sorry if that makes no sense as I'm still a bit new to these concepts!

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3 years ago
#6
(Original post by Samhil)
Ah right! So as the rocket is accelerating, then the weight force of the astronaut decreases because the gravitational pull from the earth gets weaker? I'm sorry if that makes no sense as I'm still a bit new to these concepts!

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You are right in thinking that the gravitational pull decreases as the astronaut is going away from the surface of the earth but the decrease in gravitational pull would be very small to be significant here and so can be neglected.

You know that a resultant force is required to accelerate a body, according to Newton's second Law F=ma, even if the body is in the absence of the gravitational fields. Therefore, in the case of an astronaut, before the take off of the rocket the weight of the astronaut is 750N and so when the rocket is taking off (accelerating upwards) there must be an external resultant force accelerating the astronaut. This external resultant force will appear to add to the weight of the astronaut if they were to stand on a scale in the rocket because bodies resist motion or change in motion.
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Thread starter 3 years ago
#7
(Original post by Mehrdad jafari)
You are right in thinking that the gravitational pull decreases as the astronaut is going away from the surface of the earth but the decrease in gravitational pull would be very small to be significant here and so can be neglected.

You know that a resultant force is required to accelerate a body, according to Newton's second Law F=ma, even if the body is in the absence of the gravitational fields. Therefore, in the case of an astronaut, before the take off of the rocket the weight of the astronaut is 750N and so when the rocket is taking off (accelerating upwards) there must be an external resultant force accelerating the astronaut. This external resultant force will appear to add to the weight of the astronaut if they were to stand on a scale in the rocket because bodies resist motion or change in motion.
Oh right, I think I'm beginning to understand it now! So how would you work it out? Would it be something like r-750 = 5g x mass?

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3 years ago
#8
(Original post by Samhil)
Oh right, I think I'm beginning to understand it now! So how would you work it out? Would it be something like r-750 = 5g x mass?

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When the rocket is not accelerating, the weight of the astronaut is W=mg. But when the rocket is accelerating upwards, the resultant force acting on the astronaut is F=ma.
Therefore the total force acting on the astronaut is:

F+W=ma+mg=m(a+g)

samhill: Just to let you know that you don't need to find the mass of the astronaut to work out the final force. The fact that the acceleration is 5g means that the weight will be 5 times greater than the actual weight. Therefore the total weight is 6 times the actual weight.
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Thread starter 3 years ago
#9
(Original post by Mehrdad jafari)
When the rocket is not accelerating, the weight of the astronaut is W=mg. But when the rocket is accelerating upwards, the resultant force acting on the astronaut is F=ma.
Therefore the total force acting on the astronaut is:

F+W=ma+mg=m(a+g)

samhill: Just to let you know that you don't need to find the mass of the astronaut to work out the final force. The fact that the acceleration is 5g means that the weight will be 5 times greater than the actual weight. Therefore the total weight is 6 times the actual weight.
Oh okay, thank you so much for your help!

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3 years ago
#10
anyone can help me with AS physics?

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3 years ago
#11
(Original post by swwet aish)
anyone can help me with AS physics?

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You should post your question in the study help forum, here. What is it that you are stuck on?
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3 years ago
#12
Actually im ok with the theory ! I find hard to answer past paper questions i dont understand why Posted from TSR Mobile
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3 years ago
#13
(Original post by swwet aish)
Actually im ok with the theory ! I find hard to answer past paper questions i dont understand why Posted from TSR Mobile
Maybe that's because you haven't grasped the theory quite well! Is there a question you have difficulty with?
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3 years ago
#14
(Original post by swwet aish)
Actually im ok with the theory ! I find hard to answer past paper questions i dont understand why Posted from TSR Mobile
Same, where did the OP get the question from?
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3 years ago
#15
Idk i just find all the indirect questions hard to answer in physics

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3 years ago
#16
(Original post by MaliBoy123)
Same, where did the OP get the question from?
From a book called Practice in Physics I think.
(Original post by swwet aish)
Idk i just find all the indirect questions hard to answer in physics

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You need to develop a great understanding of the theory to be able to apply it elsewhere.
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3 years ago
#17
Yu meant that i should study the theory more?

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Thread starter 3 years ago
#18
(Original post by MaliBoy123)
Same, where did the OP get the question from?
It's from Muncaster's A-level Physics book Posted from TSR Mobile
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3 years ago
#19
(Original post by swwet aish)
Yu meant that i should study the theory more?

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Yes, you should! It would be impossible not being able to apply your knowledge if you have understood the theory well enough.
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3 years ago
#20
Thanks for the help Do yu have anyone flash card or mind maps for physics?

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