JAMB Physics Past Questions & Answers - Page 83

Impulse = momentum

Impulse = Force (f) × time (t)

Momentum = mass (m) × velocity (v)

∴ Ft = Final momentum - initial momentum

FT = mv - mu

Since it is initially at rest u = 0

∴ 5 × 5 = mv − m(0)

25 = mv

∴ Final momentum = 25kgms\(^{-1}\)

c = 8µF, v = 10v

Energy stored = \(\frac{1}{2}\) cv²

= \(\frac{1}{2}\) × (8 × 10− 6) × 10²

= 4 × 10\(^{-4}\)

Eddy currents are produced by the varying flux cathode, the iron core of an equipment thus reducing efficiency due to power consumption. It can be reduced by laminating the core by breaking up the path of eddy current or by increasing the resistance of the core
Usage of insulated soft iron wire is to reduce hysteresis loss
Usage of low resistance wire (thick wire) is to reduce I2R loss
Usage of thick wire is to reduce leakage heat loss due to leakage of magnetic flux
Thus the correct answer is to use high resistance wire or thin wire

From Hoke's Law, F = ke, K = Constant of Force

For he first case, Force = mg,

= 0.8 × 10 = 8N

∴ 8 = k × 0.04

k = \(\frac{8}{0.04}\)

= \(\frac{200N}{m}\)

Since K is constant

For the second case, F = ke

F = 200 × e

∴ e = \(\frac{F}{200}\)

= \(\frac{16}{200}\)

= 0.08m

Power of a lens = \(\frac{1}{f}\)

f = focal length

f = \(\frac{1}{p}\)

= \(\frac{1}{5}\)

= 0.2m