Physics Homework - Please Help

[LadyCrazyCatLady]

DD (year 9) is really struggling with some of her physics homework and I've tried to help but to no avail. Below are the offending questions: (please help)

1. Which of the following is not a description of a closed system

a) An object that is not influenced by external effects b) A mix of objects that interact with any other object c) The behaviour of a collection of objects depends only on the other objects in the collection. d) A group of objects that don't interact with any other objects.

2.Which of the following is a correct unit for work done?
a) kg2m2/s2
b) kg m2/s
c) kg m2/s2
d) kg m/s2
DD thought the answer to be joules but that is not an option

3.Two portable phone chargers charge the same model phone (same battery capacity) from 0% to 100%. Charger A has an output power rating of 6.27W, whereas charger B has output power rating of 2.30W. How many times longer does the phone plugged into charger B take to charge compared to charger A?

Any help much appreciated.

At Yr9 she should working this out herself…
There are so many online resources available that if she puts the topic in it will provide explanations and examples she can work through, or worst case scenario she hands it in incorrectly/incomplete with the honesty she doesn’t understand

Question 1 is super straightforward, get her to read the answers slowly again. Question 2 she’s on the right track, which of the options is the same as a joule? Question 3 is a simple time ratio calculation, dividing output a by output b should get you an answer.

1. This is appropriate for year 9. She needs to know the definition of a closed system. Look that up then apply it to the possible answers.
2. this is more year 12 level work so she should find it hard. Use the equation for kinetic energy with the units rather than numbers to work it out.
3. use the equation energy=power x time to work it out.

it would be wrong of me to give her the answers and have her teacher think she can do things she can’t.

She has tried online resources and then I have also tried online resources. She has also tried emailing her teacher (no response) - mumsnet was a last resort.

She's been off school due to an operation, but is returning next week and it's assessment week so she's a bit stressed and tearful that she doesn't get it, hence my attempt to help her.

Thank you. After reading again slowly, she thinks the first answer is B.

She still can only find 'joules' as the unit for work done in her exercise book.

For C. She has got half way there, but seems stuck at 6.27 = x/time and 2.3 = x/time

I'm feeling a bit daft that I can't help her with Y9 work.

Have a look at Seneca online or Khan Academy. Free and good resources. Also Oak Continuity same sort of thing. You can also check YouTube, plenty of great physics explanations on there. For fun explanations check out Theatre of Science! Lara the tutor is super. All these are free!

Look up SI base units for Joules.

Thank you @ConBatulations - we types SI base units for Joules into Youtube and got some great explanation videos!

Thank you for the suggestions @CookiesAreForSharing we'll check those out.

b is right for 1.

make up a value for x for her pair of equations. It just needs to be the same so it doesn’t matter what she chooses.

Also, sorry that I gave the impression that I was asking you all to answer DD's homework. I realise that's exactly what a thread entitled "physics homework" suggests.

These are not questions for DD to hand in to be marked. They are example questions that have been given to all of the pupils to help them prepare ahead of assessment week. They will not be marked by the teacher, although no answers have been provided for them to check their workings against.

I'm asking for help with the questions that DD seems to have misunderstood so I can direct her to resources to help her to understand, ahead of the assessments. Getting the correct answer without understanding why she got there will not help her next week.

I'm really sorry, but if anyone is able to help with the steps for the third question or can point towards a question bank with similar questions worked through, that would be incredibly helpful.

As an (ex) Physics teacher the unit one is way too hard for year 9 and the first question is poorly written.

If she knows P=E/t, the third question is accessible.

@Justanotherteacher Ahhh...

So 10/6.27 = 1.59, 10/2.3 = 4.35 4.35/1.59 = 2.74 - so it will take 2.74times longer to charge! Thank you so much.

That’s it. As another PP said it is just ratio, but year 9s tend not to be there mathematically to understand how that works properly yet. (You can just divide the power values by each other and you’ll get the same answer.)

1A. Closed systems are just that they don’t interact with anything else
2 work done = force x distance
force =mass x acceleration thus
work done = kg ms-2 x m so kgm2 s-2 or kgm2/s2 so option c
3.- each phone charger gives a power 1 W- this is the rate of Joules per second so in any given second
A delivers 6.27 J and B delivers 2.3 J.

B will take 6.27/2.3 times as long or 2.73 times as long.

Hope that helps.

Thank you all - you're amazing.

Honestly, ChatGPT is really good at helping with this sort of thing, including follow-up questions, and requests for deeper explanations.