Physics: Post your doubts here!

[Kanekii]

View attachment 64166

I=P/S
I=E/ST
4I*0.5S=E/T
E/t=2S

 

[khadijaimran]

The increase in current suggests that the total resistance of the circuit increased(R=V/I). Now the only way the resistance can increase is through the variable resistor. So the resistance of the variable resistor was increased, and you can determine how much pd it takes up using the potential divider formula,(r1/r1+r2)*Vtotal. You can use some values to figure out that the pd of the variable resistor would increase while pd for fixed resistor would decrease. So the voltmeter readings on Q increase and for P it decreases(B).

thankyou so much

 

[hellodjfos;s'ff]

The three forces acting on a hot-air balloon that is moving vertically are its weight, the force due to air resistance and the upthrust force. The hot-air balloon descends vertically at constant speed. The force of air resistance on the balloon is F. Which weight of material must be released from the balloon so that it ascends vertically at the same constant speed?
A F
B 2F
C 3F
D 4F

I answered this a couple of days ago, so just gonna copy paste my previous explanation:
8 is a slightly tougher question. Throughout this question, the balloon is moving at a constant speed meaning the balloon is in equilibrium so upwards forces must be equal to downward forces. In the first situation, the balloon is going down so the air resistance(AR) and upthrust(UT) are acting upwards while the weight(W) is acting downwards. This making an equation, W=AR+UT. The question states that the AR has a value of F. The final equation becomes W=F+UT. For the 2nd situation, the balloon goes up, hence the W and AR act downwards while UT acts up. The equation for the 2nd equation is UT=W+AR. Now replaced W with the equation you found in the 1st situation and AR with F(as the question says). UT=F+UT+F. If you solve this equation, you will find that it would be 0=2F. This means that there is a resultant force of 2F acting downwards, so to balance it you must either produce a force of 2F acting upwards or remove a force of 2F acting downwards. The question states how much weight must be released from the balloon, so that means weight of 2F must be removed. This makes B the answer. There could be alternative methods to solve this question but I find this one to be the best.

 

[hellodjfos;s'ff]

thankyou so much

Welcome

 

[IN NEED OF HELP]

A car is moving at constant speed in a straight line with the engine providing a driving force equal to the resistive force F. When the engine is switched off, the car is brought to rest in a distance of 100 m by the resistive force. It may be assumed that F is constant during the deceleration. The process is then repeated for the same car with the same initial speed but with a constant resistive force of 0.800F. How far will the car travel while decelerating?
A 120 m
B 125 m
C 156 m
D 250 m

 

[hellodjfos;s'ff]

These are two very tough questions if you wanna practice.

 

[Kanekii]

hellp

 

[Kanekii]

These are two very tough questions if you wanna practice.

37 C?

 

[hellodjfos;s'ff]

37 C?

It's D

 

[khadijaimran]

ans is C?

 

[hellodjfos;s'ff]

View attachment 64169 hellp

Diffraction grating maxima are more spread because there are so many slits in grating than double slit, so more diffraction takes in grating hence creating more widely spread maxima. D grating maxima are sharper because again, there are so many slits in grating compared to the two in double slit, so more diffraction takes places so more waves can interfere and create a large amplitude(meaning sharper).

 

[hellodjfos;s'ff]

ans is C?

Yeah the answer is C. Just apply kirchhoff's 2nd law

 

[Kanekii]

It's D

How?

 

[Kanekii]

Shouldnt B be more close?

 

[Tom Sewage]

23: maximum pressure point is compression while minimum pressure point is rarefaction. The distance between rarefaction and compression is half the wavelength. Using v=flamda, find the wavelength and divide it by 2 to get the distance between rarefaction and compression. Wavelength will turn out to be 0.6m, so the answer is 0.3m(B).
27: you see that there is half a loop and it's a fixed string experiment. So in v=flamda, the lamda will be 0.5 which will make the equation v=0.5flamda. Now, if you want a complete wave, you would need to make the equation v=f(lamda). You can do this by increasing the frequency by 2 so that the 0.5 is cancelled out. Hence 2f is the answer(C).
28: d=1/N ---> d=1/300x1000
dsintheta=nlamda
1/300x1000 *sin90=n(600x10^-9)
n=5
This means that there are 5 orders above the central maxima and 5 below. So including the central maxima there is a total of 11 maxima(5+1+5). So the answer is C.
25: There are two sections to this question. First the train approaches the observer then the train goes away from the observer. They are asking you to find the difference in oib

Thank you soo much

 

[Tom Sewage]

need help, can anyone explain me how to solve these questions

 

[Hamnah Zahoor]

Help please?

 

[Kanekii]

View attachment 64177 Help please?

View attachment 64177 Help please?

 

[A*****]

Plz help

 

[Hamnah Zahoor]

View attachment 64178

Thankyou... I wasn't multiplying the moments by 2.