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Physics prob.....!!

B

BaKa

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a) watt the SI unit of power and it is the rate of transfer of energy of 1 Joules per second ie Watt = 1 J/s
b i) tension in cable = weight of the lift = mg which is 580 x 10 (going up gravitational) = 5800
ii) increase in P.E = mgh = 580x10x12 = 69600 J (remember to give the Si unit)
iii) efficiency = output power/input power x 100 = (69600/15s)/6200 (given in the question) = 4640/6200x100 = 75%

u know u should learn the formulas by heart it will be easy when doing questions like these if u do :)
 
sksuriza

sksuriza

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(a)power is watt.
a power of 1 watt is used to do 1 j of work in 1 sec

(b) i) tension is force
F=ma
=580x10
=5800N
ii) P.e=mgh
=580x10x12
=69600J
iii) power=energy/time
=69600/15
=4640W

efficiency= power output/power input x 100%
=4640/6200 x 100%
=74.8%
 
B

BaKa

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a) the lines should be pointing towards the magnet (as said in the question the needle is a small magnet) so it should point in the south of the magnet ie towards the magent.
b) lets see (easiest part) hmmm... when the switch is closed the soft iron core acts as a magnet due to electromagnetic induction introduced into it by the electricity flowing throught the coil. the soft iron core acting as a magnet attracts the pivot soft iron towards itself and the other part of the pivot pulls up and the contacts become closed. ( u could also mention an example ie a household bell)
c i) when light falls on the ldr the resistance decreases (also the same case with a thermister)
ii) this needs a diagram to explain complete but hope u understand. connect the lamp with the points from C (in the diagram) and place a battery under the lamp and then connect the battery's other point ie negetive to the closing point of C or u can say the relay.

hope this helped
 
M

maestro007

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11 (b) (ii) it will be a curve starting from the origin and going parrallel to the x-axis.
like:
 
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