Physics 1st Paper CQ-Jessore Board-2017

1. Mass of a simple pendulum's bob is $1.2 \times$ $10^{-2} \mathrm{~kg}$. It is swinging at an amplitude of $51 \mathrm{~mm}$. It takes $49.75 \mathrm{sec}$ to complete 25 oscillation. Radius of earth is 6.4 $\times 10^{6} \mathrm{~m}$.

2. A student, keeping the pressure constant, increased the temperature of some $\mathrm{O}_{2}$ gas which was initially in ideal temperature. So, the volume doubled. And so his friend said that the mean square velocity of the molecules of experimented gas will be doubled too.

3. A $30 \mathrm{gm}$ marble hit another stationary marble at $10 \mathrm{~ms}^{-1}$ velocity. After the collision, first marble lost its $75 \%$ velocity, the latter marble gained $9 \mathrm{~ms}^{-1}$ velocity and hit a clay wall at $3 \mathrm{~m}$ distance. The obstructing force of the wall is $3 \mathrm{~N}$. (Ignoring the air resistance)

4. According to the picture, a boat is moving from position $A$ toward $A D$ of another side of a river, which has $2.5 \mathrm{~km}$ width.

Velocity of the boat on steady water $=(3 \hat{\mathrm{i}}+3 \hat{\mathrm{j}}) \mathrm{m} \cdot \mathrm{s}^{-1}$ and velocity of tide $=2 \hat{i} \mathrm{~m} \cdot \mathrm{s}^{-1}$. In another case the boat is rowed along AB at the same speed.

5. A heavy $250 \mathrm{~N}$ symmetrical object $\mathrm{XY}$ is hanged from two equally long wires A and B horizontally. It is shown in the diagram (uncompressed state). Cross sectional area of each wire is $2.5 \times 10^{-7} \mathrm{~m}^{2}$. B wire's longitudinal strain is $2.5 \times 10^{-4} \mathrm{~m}^{2}$, A wire's $0.8 \mathrm{~m}$ is made of brass and the rest is steel.

Young's modulus for steel $=2 \times 10^{11} \mathrm{~Pa}$

Young's modulus for brass $=1 \times 10^{11} \mathrm{~Pa}$