Physics: Post your doubts here!

[Keirad]

Need help...
A ball is falling at terminal speed in still air. The forces acting on the ball are upthrust, viscous
drag and weight.
What is the order of increasing magnitude of these three forces?
A upthrust → viscous drag → weight
B viscous drag → upthrust → weight
C viscous drag → weight → upthrust
D weight → upthrust → viscous drag

Answer is A. But why?
Thank you !

The upthrust will be the lowest because the force from the atmosphere pushing you upwards is the least as the atmosphere is very thin. The weight will be the greatest because it is the force that is making you fall down .

 

[Keirad]

Can someone explain Q 33 May June 2006 P1. I am not understanding how it will be a potential divider circuit and how to solve it.

 

[Charlotte20102013]

Can someone explain Q 33 May June 2006 P1. I am not understanding how it will be a potential divider circuit and how to solve it.

Thanks for the explanation.
As for your question,
Refer to solution 100 at
http://physics-ref.blogspot.com/2014/11/physics-9702-doubts-help-page-19.html
They are similar.
See if it helps.

 

[Keirad]

Thanks for the explanation.
As for your question,
Refer to solution 100 at
http://physics-ref.blogspot.com/2014/11/physics-9702-doubts-help-page-19.html
They are similar.
See if it helps.

Thanks
It really helped me to understand how to obtain the answer

 

[Riding hood]

Please help me with this.. I am very confused!

 

[PlutoHuman]

CORRECT ME IF I AM WRONG..... the answer to this question is C because we have to take the perpendicular distances between the slopes.......RIGHT?

 

[Awesome12]

CORRECT ME IF I AM WRONG.....View attachment 49325 the answer to this question is C because we have to take the perpendicular distances between the slopes.......RIGHT?

Yeah. You assume one of the points to be the pivot.

Take the topmost point as the pivot. Now you need the PERPENDICULAR DISTANCE, from the force to the pivot.

Let the PERPENDICULAR DISTANCE = x

Sin 50 = x / 0.30

x = 0.2298 = 0.23


Now F * PERPENDICULAR DISTANCE

2 * 0.23

=0.46 Nm

 

[PlutoHuman]

Yeah. You assume one of the points to be the pivot.

Take the topmost point as the pivot. Now you need the PERPENDICULAR DISTANCE, from the force to the pivot.

Let the PERPENDICULAR DISTANCE = x

Sin 50 = x / 0.30

x = 0.2298 = 0.23


Now F * PERPENDICULAR DISTANCE

2 * 0.23

=0.46 Nm

Thank u!

 

[princess Anu]

..

 

[mohammad hurani]

Part (ii) Please explain
thank u

 

[mohammad hurani]

with explanation plz

 

[Charlotte20102013]

Can someone help with these...
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s13_qp_13.pdf
Q3 (Ans: C) (I chose D)
Q11 (Ans: A)
Q17 (Ans: C) (I chose D cz I thought molecules in solids (ice) are closer together??)
Thanks.

 

[FrostBite92]

A thermometer can be read to an accuracy of ± 0.5 °C. This thermometer is used to measure a
temperature rise from 40 °C to 100 °C.
What is the percentage uncertainty in the measurement of the temperature rise?

Can anyone HELP me answer this???It's so frustrating...
Appreciate the help

 

[Charlotte20102013]

3 and 11 are answered as solution 151 and 162 at
http://physics-ref.blogspot.com/2014/11/physics-9702-doubts-help-page-26.html
http://physics-ref.blogspot.com/2014/11/physics-9702-doubts-help-page-27.html

respectively

Thank you!

 

[Charlotte20102013]

A thermometer can be read to an accuracy of ± 0.5 °C. This thermometer is used to measure a
temperature rise from 40 °C to 100 °C.
What is the percentage uncertainty in the measurement of the temperature rise?

Can anyone HELP me answer this???It's so frustrating...
Appreciate the help

The uncertainty in each thermometer reading is 0.5 °C. Question asked for percentage uncertainty in temperature rise. To calculate the temperature rise you take 100-40=60 °C, and that's the differnece between two thermometer readings. When you add or subtract two quantities, their absolute uncertainty should be added together.

So here, the total absolute uncertainty is 0.5+0.5=1.0 °C.

And the PERCENTAGE uncertainty in temp rise would be (absolute uncertainty/temp rise)*100%
Thus, you get (1/60)*100%= 1.7%

 

[Charlotte20102013]

http://freeexampapers.automaticpapers.com/as-a-level/physics-9702/9702_s14_qp_12.pdf
Q27 (Ans: D)
Q34 (Ans: D) (How does V1 and V2 vary as light intensity increase/decrease? Do they increase and decrease together?)
Urgent help needed. Please and thank you!

 

[hassan.arif.12]

An aeroplane travels at an average speed of 600 km h–1 on an outward flight and at 400 km h–1 on
the return flight over the same distance.

What is the average speed of the whole flight?
A 111 m s–1 B 167 m s–1 C 480 km h–1 D 500 km h–1

can any one answer this question??

For simplicity's sake, let's assume the distance travelled is 1,200 km.

outbound - 600 km / h
return - 400 km / h

total time: 1 + 1.5 = 2.5 hrs

1200/2.5 = average speed

 

[hassan.arif.12]

help!!!!
Q) A steel spring has a spring constant of 150 N m–1. When a 25 N weight is hung from the spring, it
has a stretched length of 55 cm.
What was the original length of the spring?

A 0.38 m B 0.49 m C 0.61 m D 0.72 m

 

[Rohaan Nadeem]

help!!!!
Q) A steel spring has a spring constant of 150 N m–1. When a 25 N weight is hung from the spring, it
has a stretched length of 55 cm.
What was the original length of the spring?

A 0.38 m B 0.49 m C 0.61 m D 0.72 m

F=kx
for a force of 25N
x=25/150 = 1/6 m.
Now, stretched length= original length + x
Therefore Original length = .55-.17 = .38m......(A)

 

[Paris Palmer]

F=kx
for a force of 25N
x=25/150 = 1/6 m.
Now, stretched length= original length + x
Therefore Original length = .55-.17 = .38m......(A)

In simple harmonic motion, one of the formulas of Time period of a pendulum is (T=2 pi underoot l/g)
If a lift is moving with upward acceleration, a, then a pendulum inside it will have g=9.81+a because of the total value of g, acceleration of 9.81 m/s sq. was used to cancel acceleration due to gravity so it will also be added into a.
But if a lift is moving with downward acceleration, a, why will the value of g be 9.81-a?