**31. **Two objects P and Q of masses 100kg and 20kg respectively are 1.2m apart on a horizontal surface. Calculate the net gravitational force acting on Q. \([G= 6.67 \times 10^{-11} Nm^{2}kg^{-2}]\)

**A.**\(1.11\times 10^{-7} N\) towards P**B.**\(1.11\times 10^{-7} N\) towards Q**C.**\(9.26\times 10^{-8} N\) towards P**D.**\(9.26\times 10^{-8} N\) towards Q

**Correct Option: Answer is D**

\(F= \frac{Gm_{1}m_{2}}{r^{2}}\)
\(m_{1} = 100kg\)
\(m_{2} = 20kg; r =1.2m\)
\(G= 6.67\times 10^{-11}\)
\(F = \frac{6.67\times 10^{-11}\times 100\times 20}{(1.2)^{2}} = 9.26\times 10^{-8}\)
The acceleration of each object is inversely proportional to the mass, the lighter object will move a bit faster, hence. the force will act in the direction of Q.**32. **The primary of a transformer has 100 turns and its secondary has 200 turns. If the voltage at the primary is 100V, determine the voltage at the secondary.

**A.**50V**B.**100V**C.**200V**D.**400V

**Correct Option: Answer is C**

The ideal transformer (either step-up or step-down) works with the equation:

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

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.

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

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

**33. **In the diagram illustrated a block of mass M is at rest on a plane inclined at an angle $\theta $ to the horizontal. As θ$\theta $ increases, the velocity ratio of the plane

**A.**increases**B.**decreases**C.**remain the same**D.**decreases and later increases

**Correct Option: Answer is B**

The velocity ratio and therefore, the mechanical advantage of an inclined plane system increases as θ$\theta $ decreases and vice-versa.

**34. **When the speed of a car is halved, its kinetic energy is

**A.**doubled**B.**quartered**C.**halved**D.**quadrupled

**Correct Option: Answer is B**

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

When v is halved, we have

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

= \(\frac{K_{1}}{4}\)

Hence, the initial kinetic energy is quartered.

**35. **A wire of length 400cm is stretched between two fixed points. When plucked, its fundamental frequency is 150Hz. Calculate the speed of the wave produced.

**A.**250ms−1**B.**625ms−1**C.**1200ms−1**D.**1500ms−1

**Correct Option: Answer is C**

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

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

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

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

**36. **

The diagram above illustrates a waveform. Determine the number of wavelengths in it

**A.**4**B.**3 1/2**C.**2 1/2**D.**2

**Correct Option: Answer is C**

**37. **A resistor with fixed resistance value is called a

**A.**resistance box**B.**standard resistor**C.**shunt resistor**D.**multiplier resistor

**Correct Option: Answer is B**

**38. **Which of the following statements is not an advantage of an alkaline accumulator?

**A.**The electrolyte does not need attention**B.**It can be recharged**C.**It has low internal resistance**D.**It has a much longer life than lead-acid accumulator

**Correct Option: Answer is A**

**39. **The diagram above illustrates the wire connections to a three-pin plug. The wires P, Q and R respectively are:

**A.**live, neutral and earth**B.**neutral, earth and live**C.**earth, live and neutral**D.**earth, neutral and live

**Correct Option: Answer is B**

**40. **Which of the following statements about parallel plate capacitors is/are correct?

I. Capacitance of the capacitor is inversely proportional to the distance between the plates

II. Capacitors can filter a.c signals from d.c

III. Capacitors can store charges

**A.**I only**B.**I and II only**C.**II and III only**D.**I, II and III