21. The pitch of an acoustic device can be increased by

**A.**decreasing the loudness**B.**increasing the intensity**C.**increasing the frequency**D.**decreasing the intensity

**Correct Option: Answer is C**

**pitch**of a sound. A high

**pitch**sound corresponds to a high frequency sound wave and a low

**pitch**sound corresponds to a low frequency sound wave. … Such sound waves form the basis of intervals in music.

**22. **One of the features of the fission process is that

**A.**it leads to chain reaction**B.**its products are not radioactive**C.**neutrons are not released**D.**the of the masses of the reactants equals the sum of the masses of the products

**Correct Option: Answer is A**

**23. **The linear expansivity of brass is 2 x 10\(^{-5}\) C\(^{-1}\). If the volume of a piece of brass is 15.00cm at 0°C, what is the volume at 100°C

**A.**16.03cm\(^3\)**B.**15.09cm\(^3\)**C.**16.00cm\(^3\)**D.**15.03cm\(^3\)

**Correct Option: Answer is B**

Volume Expansivity \(\gamma\) = \(3\alpha\)

\(\gamma = 3 \times 2\times10^{-5}\)

\(\gamma = 6\times10^{-5}C^{-1}\)

\(V_{2} = V_{1}(1 + \gamma\theta)\)

\(V_{2} = 15( 1 + (6\times10^{-5}\times(100-0)))\)

\(V_{2} = 15(1.006)\)

= \(15.09cm^{3}\)

**24. **A lead bullet of mass 0.05 kg is fired with a velocity of 200 m/s into a lead block of mass 0.95 kg. Given that the lead block can move freely, the final kinetic energy after impact is

**A.**100J**A.**150J**C.**50J**D.**200J

**Correct Option: Answer is C**

From the law of conservation of linear momentum,

\(m_1 u_1 + m_2 u_2 = m_1 v_1 + m_2 v_2\)

Since the collision is inelastic, we have

\((0.05 \times 200) – (0.95 \times 0) = (0.05 + 0.95)V\)

\(10 = V\)

\(V = 10ms^{-1}\)

Hence the Kinetic energy = \(\frac{1}{2} (0.05 + 0.95) \times 10^2\)

= \(\frac{1}{2} \times 100\)

= 50J

**25. **In a series R-L-C circuit at resonance, the voltages across the resistor and the inductor are 30V and 40V respectively. What is the voltage across the capacitor?

**A.**30V**B.**70V**C.**50V**D.**40V

**Correct Option: Answer is D**

**26. **If the fraction of the atoms of a radioactive material left after 120years is $\frac{\mathrm{1/}}{64}$, what is the half-life of the material? $\frac{\mathrm{1/}}{64}$

**A.**20 years**B.**10 years**C.**2 years**D.**24 years

**Correct Option: Answer is A**

**27. **

In the diagram shown, which of the simple pendulum will resonate with P when set into oscillation?

**A.**U**B.**T**C.**R and T**D.**Q and R

**Correct Option: Answer is B**

**28. **The time rate of loss of heat by a body is proportional to the

**A.**temperature of its surroundings**B.**temperature of the body**C.**difference in temperature between the body and its surroundings**D.**ratio of the temperature of the body to that of its surroundings

**Correct Option: Answer is C**

**29. **A positively charged rod X is brought near an uncharged metal sphere Y and is then touched by a finger with X still in place. When the finger is removed, the result is that Y has

**A.**no charge and a zero potential**B.**a positive charge and a zero potential**C.**a negative charge and a positive potential**D.**a negative charge and a negative potential

**Correct Option: Answer is D**

**30. **Electrical appliances in homes are normally earthed so that

**A.**a person touching the appliances is safe from electric shock**B.**both the a.c. and d.c. sources can be used**C.**the appliances are maintained at a higher pd than the earth**D.**the appliances are maintained at a lower pd than the earth