Answers

How to prepare for IIT JEE?

Surya Kant Dwivedi asks: “I am always confused in Physics that how can i do my best in Physics. It is my weakest portion in ’PCM’. Please guide me.”

Excelling in Physics in IIT JEE requires systematic planned preparation. The first step is to make sure that you can solve all the exercises from NCERT text book (including the solved examples and additional exercises) confidently and completely. This ensures that you have sufficient exposure and you are up to the standard expected of you.

The next step is to get a good collection of questions asked previously in IIT JEE and solve them. If you are not able to solve a problem, you are welcome to post it here.

Recommended Books:

Fundamentals of Physics (Resnick Hallidey)

Concepts of Physics (HC Verma)

Irodov Problem in Physics

A Numerical Problem from Projectile Motion

A short is fired from a gun on the top of a hill 90m high with velocity 80m/s at an angle of 30 degree with the horizontal. Find the horizontal distance between the vertical line through the gun and the ponit where the shot strikes the ground? (Shilpa asked this question)

Answer:

Take S_y= -90m

ay= -g=-9.8m/s²

u_y= u sin(30) =80 x 0.5 = 40m/s

Substitute in the eqn

s = ut + 0.5 at²

and find t

The horizontal distance Rx = horizontal velocity x time =  U cos (30) x time

Substitute for u and t and get the answer

Is the equation for displacement in the n th second dimensionally correct?

Is the equation for displacement in the n th second dimensionally correct?

S = u + a (n- 1/2)

Answer:

Yes

See the explanation given by Vimal Raj

If we notice the derivation of this formula
let t1=x and t2=y (for my easiness)
S(y)=uy + 1/2 ay^2———-(1)
S(x)=ux + 1/2 ax^2———–(2)
sub (2) from (1)
S(y)-S(x)=uy + 1/2 ay^2 – ux – 1/2 ax^2
S(y)-S(x)=u(y-x)+a/2(y^2-x​^2)
here we know y-x =1 s ,then
Sn = u (1s) + a/2(y+x)(y-x)
Sn =u(1s) + a/2(y+x)(1s)

Dimension of Sn must be equal to u(1s)

u=LT^1
THEN Sn=[LT^1][T]=[L]

(Also Visit https://www.facebook.com/groups/askphysics/ for obtaining help from the Facebook group members)

Dimensions of angle, specific heat, heat, latent heat, frequency, charge, potential difference, resistance.

What are the dimensions of angle,specific heat,heat,latent heat,frequency,charge,potential difference,resistance?

• Angle does not have any dimension as it is a pure ratio
• Dimensions of Specific heat  = [M⁰L²T^-2K^-1]
• Heat has the same dimensional formula as that of energy [ML²T^-2]
• Latent heat is the heat energy required to convert unit mass of a substance from one state to another without change in temperature. Therefore, the dimensions are [M⁰L²T^-2]
• Dimensions of frequency = [M⁰L⁰T^-1]
• Dimensions of charge = [AT]
• Dimensions of potential difference = [ML²T^-3A^-1]
• Dimensions of [ML²T^-3A^-2]

What is meant by charge on a capacitor?

Mohit asked this question:

“What is meant by charge on a capacitor?”

Answer: As we know, a simple capacitor (say a parallel plate capacitor) consists of two plates parallel to each other. When charged, charge on either plate of the capacitor is called charge on the capacitor.

The following links will help you explore further and understand more

• http://www.kpsec.freeuk.com/components/capac.htm
• http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capac.html
• http://www.youtube.com/watch?v=zNpbdptwxlQ
• http://www.youtube.com/watch?v=qdXbnhb1bVo&feature=related

Addition of vectors – can you add 3 unit vectors to get a unit vector ?

“Can you add 3 unit vectors to get a unit vector ? discuss in terms of velocity, force etc”

-Sindhuja posted

The answer is yes. Please find a detailed description on addition of vectors with examples and exercises at the following links.

• http://www.physchem.co.za/Vectors/Addition.htm
• http://www.physchem.co.za/Vectors/Physical%20Examples.htm
• http://www.physicsclassroom.com/class/vectors/u3l1b.cfm
• http://www.walter-fendt.de/ph14e/resultant.htm
• http://canu.ucalgary.ca/map/content/vectors/addition/explain/tiptail/
• http://www.physicsclassroom.com/morehelp/vectaddn/practice.cfm