2018 - WAEC Physics Past Questions and Answers - page 4

\(F= \frac{Gm_{1}m_{2}}{r^{2}}\)

\(m_{1} = 100kg\)

\(m_{2} = 20kg; r =1.2m\)

\(G= 6.67\times 10^{-11}\)

\(F = \frac{6.67\times 10^{-11}\times 100\times 20}{(1.2)^{2}} = 9.26\times 10^{-8}\)

The acceleration of an object is inversely proportional to its mass. Hence, the lighter the object the faster it can move... the force will act in the direction of Q.

The equation of ideal transformer:

\(\frac{V_{s}}{V_{p}} = \frac{N_{s}}{N_{p}} = \frac{I_{p}}{I_{s}}\)

where \(V_{s}\) and \(V_{p}\) are the voltages applied to the secondary and the primary respectively

\(N_{s}\) and \(N_{p}\) are the number of turns on the secondary and primary coils respectively

\(I_{p}\) and \(I_{s}\) are the currents flowing in the primary and secondary coils respectively.

\(\frac{V_{s}}{100} = \frac{200}{100}\)

\(V_{s} = \frac{200\times 100}{100} = 200V\)

Given \(K_{1}\) = \(\frac{mv^{2}}{2}\).

When v is halved, we have

\(K_{2}\) = \(\frac{m\times (\frac{v}{2})^{2}}{2}\)

= \(\frac{K_{1}}{4}\), which is a quater

The fundamental frequency \((f_{0})\) = \(\frac{v}{2l}\)

\(f_{0} = 150Hz; l =400cm = 4m\)

\(150 = \frac{v}{2\times 4}\)

\(v = 150 \times 8 = 1200ms^{-1}\)

Capacitors pass AC but block DC signals (when charged up to the applied DC voltage). They are often used to

• separate the AC and DC components of a signal
• store energy