https://isaacphysics.org/questions/pendulum_pair?board=d43a5a20-2f1c-4df2-a833-a457bf2cb206&stage=a_level

I've tried to just difference the times but I feel like im missing another equation to use or im doing smth wrong. Any help would be greatly appreciated.

I've tried to just difference the times but I feel like im missing another equation to use or im doing smth wrong. Any help would be greatly appreciated.

Working:

Original post by mosaurlodon

Working:

2pisqrt(l/g)

and you want to think about how the period(s) relate to breaking the laser beam for the two pendulums. The actual perturbation is a bit of a red herring.

Also the hints suggest thinking about the shorter pendulum first, then the longer one and thats a good hint.

(edited 2 months ago)

ok I've considered the shorter pendulum first:

Though now im not sure what the time difference represents - is this value equal to 0.3s - how is the difference between the times determined?

Though now im not sure what the time difference represents - is this value equal to 0.3s - how is the difference between the times determined?

Original post by mosaurlodon

ok I've considered the shorter pendulum first:

Though now im not sure what the time difference represents - is this value equal to 0.3s - how is the difference between the times determined?

Though now im not sure what the time difference represents - is this value equal to 0.3s - how is the difference between the times determined?

Id use a more descriptive label(s) for time, so 1/4 period until it first cuts, then 3/4 period until it cuts again or by symmetry, 0.3 s must be a 1/2 period.

Then think about the second pendulum and how to minimise the (total) length.

(edited 2 months ago)

Ok I think I get what the question is asking?

So the time taken for the first pendulum to complete a half period is 0.3s so I can work out l1.

In this time the second pendulum completes a quarter period barely reaching the laser (which I think would give the lowest length) so I can work out l2.

So the time taken for the first pendulum to complete a half period is 0.3s so I can work out l1.

In this time the second pendulum completes a quarter period barely reaching the laser (which I think would give the lowest length) so I can work out l2.

Original post by mosaurlodon

Ok I think I get what the question is asking?

So the time taken for the first pendulum to complete a half period is 0.3s so I can work out l1.

In this time the second pendulum completes a quarter period barely reaching the laser (which I think would give the lowest length) so I can work out l2.

So the time taken for the first pendulum to complete a half period is 0.3s so I can work out l1.

In this time the second pendulum completes a quarter period barely reaching the laser (which I think would give the lowest length) so I can work out l2.

Oh It just clicked! Thank you!

Original post by mosaurlodon

Oh It just clicked! Thank you!

I am still confused what is exact answer of total minimum length

Original post by mosaurlodon

Oh It just clicked! Thank you!

what is answer

If you post your working I can try to point you in the right direction

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