Transcript P2 Calculations - the Redhill Academy

P3 Calculations
The speed of sound in the steel is 6000m/s.
What is the distance to the flaw?
s=vxt
s = 6000 x (5 x 0.000005)/2
s = 0.075m
Remember to
halve the time
Calculate the magnification of the lens ?
M= Image Height
Object Height
M= 18/6
M=3
Calculate the weight of the boy
Clockwise Moment = Anticlockwise moment
360 + 1.6W = 960
1.6W = 600
W = 375 N
If the pendulum takes 20 seconds to complete 10
swings what is its frequency ?
Time period = 2 seconds
f= 1/T
f=1 / 2 = 0.5 Hz
Area = 5
cm2
Force = 20N
Area = 25 cm2
What is the force exerted by the large cylinder?
Pressure on small cylinder = F/A = 20/5 = 4N/cm2
So Pressure on large cylinder = 4N/cm2
Force = P x A = 4 x 25 = 100 N
In the National Grid, very large step-up transformers link
power stations to the transmission cables.
A transformer used for this purpose has 800 turns on its
primary coil and 12 800 turns on its secondary coil. The
p.d. (potential difference) across its primary coil is 25 kV.
Calculate the p.d. across its secondary coil
Vp= Np
Vs= Ns
25000 = 0.0625
Ns
25000 = 800
Ns
12800
25000 = Ns
0.0625
25000 = 0.0625
Ns
400,000 = Ns
Calculate the refractive index of glass
Refractive index = sini
sin r
Refractive index = 0.87 / 0.57
Refractive index = sin60o Refractive index = 1.52
sin34.5o
Critical angle = 42o
Calculate the refractive index of glass
Refractive index =
1
Refractive index = 1.49
sin c
Refractive index =
1
sin 42o
What is the power of a convex lens of focal length
20cm ?
Power =
Power =
1
f
Refractive index = 1.49
1 = +5 Diopters
0.2
What is the power of a concave lens of focal
length 20cm ?
Power =
Power =
1
f
Refractive index = 1.49
1 = -5 Diopters
0.2
If the primary current is 2.5 A what is the current
in the secondary?
Vp x Ip= Vs x Is
25 = Is
20
10 x 2.5= 20 x Is
1.25A = Is
25 = 20 Is