Physics MCQs help needed

[workaholic]

Plz explain this mcq.
Which statement describes how the steel bar can be demagnetised?
A Reverse the d.c. supply and gradually decrease the current in the circuit.
B Reverse the d.c. supply and gradually increase the current in the circuit.
C Use an a.c. supply and gradually decrease the current in the circuit.
D Use an a.c. supply and gradually increase the current in the circuit.

i dont understand y one shud decrease current and not increase
Answer is C....

This also
13 A parachutist has opened his parachute and is falling to Earth at constant speed.
What is the principal energy conversion taking place as he falls?
A kinetic energy → potential energy
B kinetic energy → thermal energy (heat)
C potential energy → kinetic energy
D potential energy → thermal energy (heat)

Shouldnt the answer be C. It says D in the mark scheme.
Plz explain...

 

[adnanj]

i don;t have explanation for the first mcq..
but for the second it cannot be converted to kinetic energy because the speed is CONSTANT...
I hope u get my point

 

[VelaneDeBeaute]

Plz explain this mcq.
Which statement describes how the steel bar can be demagnetised?
A Reverse the d.c. supply and gradually decrease the current in the circuit.
B Reverse the d.c. supply and gradually increase the current in the circuit.
C Use an a.c. supply and gradually decrease the current in the circuit.
D Use an a.c. supply and gradually increase the current in the circuit.

i dont understand y one shud decrease current and not increase
Answer is C....

This also
13 A parachutist has opened his parachute and is falling to Earth at constant speed.
What is the principal energy conversion taking place as he falls?
A kinetic energy → potential energy
B kinetic energy → thermal energy (heat)
C potential energy → kinetic energy
D potential energy → thermal energy (heat)

Shouldnt the answer be C. It says D in the mark scheme.
Plz explain...

I dont know...the first question appeared in our mocks and i chose D and it was correct..!
Sumone 4m A-lvls wud explain it better perhaps..!

 

[BaKa]

lol its easy first ill explain the second one.

kinetic energy is only used for objects moving on a strait forward direction and not from upwards to downwards so its D as when he comes down (as seen in movies the tip get heated up) the energy acts on it and due to air friction the objects tends to heat up.

ok well by my thoughs i first chose C and i was correct. the principal behind is that ac has both positive and negative current flowing in it so when u increase it the electromagnet also get more magnetised so it could not be D and if u decrease it (the same case with coil and solonoid) the electricity flowing though it would decrease and take away any charges and the magnetic steel would loose its magnetism.

that was easy...

 

[mury456]

som1 help me out with this and explain the answer !!!

 

[xhizors]

A is the ans for last one use right hand grip rul point the thumb in the direction of convectional current and gripping will be the field

 

[xhizors]

Q 25 and 31 from 5054/12/O/N/10

 

[adnanj]

B is the correct answer..! its wire carrying current inside the paper..!

 

[Muhammad Talha]

B is the correct answer.....

 

[Silent Hunter]

ya B

 

[Silent Hunter]

ANY BODY HELP IN http://www.xtremepapers.me/CIE/Cambridg ... 5_qp_1.pdf MCQ 28

 

[sweetiepie]

itx B...