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F=ma

I have done two of these questions and i got them both wrong and i have no clue what I'm doing wrong and I'm using the f=ma formula. I'll post rhe question below appreciate any help

Reply 1

A0W0N

i used the same method for both questions

Reply 2

chrismanning0711

Try 4.0 and 2000.0 also 4.00 and 2000.00

Reply 3

A0W0N

Original post by chrismanning0711

Try 4.0 and 2000.0 also 4.00 and 2000.00

didn't work :frown:

Reply 4

TheCoolBro

Your answers are right! That's so dumb that it doesn't work bro

Reply 5

Anon#9

You didn't calculate the weight of the objects. The total force of resistance is----> F+Weight
F in this case is F=ma. You have calculated F, but you haven't calculated the weight. Try calculating the weight and add it with F to get the final answer.
I hope that this will work out.
@A0W0N

(edited 3 years ago)

Reply 6

Anon#9

Original post by TheCoolBro

Your answers are right! That's so dumb that it doesn't work bro

No bro, it's not right.

Reply 7

chrismanning0711

Original post by Sam_R9

No it's already given you the overall acceleration which includes the acceleration due to gravity so adding that again would be wrong

Reply 8

Anon#9

Original post by chrismanning0711

No it's already given you the overall acceleration which includes the acceleration due to gravity so adding that again would be wrong

Just try my method. It'll work out because you have only calculated the force. You haven't considered the weight.
It doesn't include the acceleration due to gravity. The acceleration is only about the object. That acceleration would be obtained by throwing. It's not bcoz of the gravity.
Try my method and then tell me if it's wrong or not :wink:

Reply 9

AGrizzlyBearo

You've calculated the resultant force and used it as your answer, but you need to find the resistive force.

Drawing force diagrams for these sort of questions can be useful.

(edited 3 years ago)

Reply 10

A0W0N

i added it and subtract it and i got the wrong answer I'm still confused

Original post by A0W0N

i added it and subtract it and i got the wrong answer I'm still confused

In your above working out, I think you've written the calculation as:
(2 x 9.8) -4 =19.6
However,
(2 x 9.8) -4 = 15.6 ( I think you didn't type in the -4 on your calculator).
If this is the right answer, then your method is correct, it's just a small calculation error :smile:

Reply 12

simon0

Original post by A0W0N

i added it and subtract it and i got the wrong answer I'm still confused

Your diagram is correct, well done.

However, your calculation is not.
Note Newton's Second Law:

\boldsymbol{F_{\textrm{Net / Resultant}}} = m \boldsymbol {a} .

Note vectors F and a and note the Net/Resultant force.

--------------------------------------------------------------------------------------------

We have forces:
- Weight 2g acting downwards,
- Resistance R acting upwards,

as well as acceleration 2 m/s^{2} downwards.

Resolving downwards (we can resolve upwards as well, up to you) we have:

2g - R = 2 * 2 = 4 .

Can you re-arrange to find R?

----------------------------------------------------------------------------------------------

Also similar setup for your second question where I advise to draw a diagram and resolve up or down.

(edited 3 years ago)

Reply 13

Anon#9

Original post by AGrizzlyBearo

You've calculated the resultant force and used it as your answer, but you need to find the resistive force.

Drawing force diagrams for these sort of questions can be useful.

I actually forgot to mention it as resultant force. Idk y I forgot that, it's been a year since I've practiced physics but I still remember some principles :redface: