AP Physics free response practice help

[harmonicmotion]

sorry for the random letters your responses don't come up on my comp otherwise

 

[harmonicmotion]

wait so would dv/dt just be 8/(1+5t)

 

[harmonicmotion]

hsjsysgdsd

 

[arildno]

sorry for the random letters your responses don't come up on my comp otherwise

I understand.

Now, as for d) assuming you manage c), it is perhaps simplest to remember that the impulse over a time interval equals the change in momentum over that interval.

 

[harmonicmotion]

dhdyegstdff

 

[arildno]

wait so would dv/dt just be 8/(1+5t)

No, that is v itself!

You must differentiate that expression to get the acceleration.

 

[harmonicmotion]

isnt impulse also force times the change in time

 

[harmonicmotion]

sorry i still can't figure out c

 

[arildno]

isnt impulse also force times the change in time

Only if the force is constant.
If it is not constant, you must perform the integral of F over time.
Happily, this equal to the change of momentum over that time.

 

[harmonicmotion]

hdysudjfgf

 

[arildno]

sorry i still can't figure out c

Well, what is v?

differentiate that function!

 

[harmonicmotion]

for c i got (500)(-40)(1+5t)^-2

 

[arildno]

Oops!
Remember that the mass of the system consists of BOTH the masses, i.e, 1000+500=1500.

 

[harmonicmotion]

gyhtdesrehh

 

[harmonicmotion]

so for 500 i put 1500 and then its right?

 

[arildno]

so for 500 i put 1500 and then its right?

That is correct.

 

[harmonicmotion]

hyujiklofddss

 

[harmonicmotion]

so d is (mv(final)-mv(initial))/(time)

 

[arildno]

No, that would give you the average FORCE over that time interval.
Do not divide with time; the impulse is just the momentum difference.

 

[harmonicmotion]

hyhndhstsy

 

[harmonicmotion]

so 3000?

 

[harmonicmotion]

hyujhjyuhj

 

[harmonicmotion]

mkinjubhyt

 

[harmonicmotion]

wait sorry i messed up

 

[harmonicmotion]

-10909.09?

 

[harmonicmotion]

nhymjumjuy

 

[arildno]

wait sorry i messed up

Indeed you did.

You should get:

$$I=1500*(\frac{8}{11}-8)=-1500*\frac{80}{11}$$

 

[harmonicmotion]

asdfghjkl;

 

[harmonicmotion]

oh ok thank you so much!

 

[arildno]

oh ok thank you so much!

You're welcome!