Four masses each 2 kg are placed at the corners A, B, C, D of a mass less square frame. 40 kg mass is at the centre O of a square frame of side 0.2 m . It is to be rotated about an axis passing through the centre O and perpendicular to the plane of the frame. Calculate the torque in $\mathrm{N}-\mathrm{m}$ required to produce an angular acceleration of $\frac{\pi}{2} \mathrm{rads}^{-2}$.
$\frac{\pi}{25}$
$\frac{\pi}{12.5}$
$\frac{2 \pi}{12.5}$
$\frac{2 \pi}{25}$
Two identical charged spheres are suspended by strings of equal lengths. The strings make an angle of $45^{\circ}$ with each other. When the system is immersed in a liquid of relative density 0.8 , the angle between the strings remains unchanged. If the density of the material of the sphere is $2.4 \mathrm{gcm}^{-3}$, what is the dielectric constant of the liquid?
1.6
1.5
0.5
2
A car, starting from rest, accelerates at a rate of $\beta$ through a distance S , then continues at constant speed for time t and then decelerates at a rate of $\frac{\beta}{2}$ to come to rest. If the total distance travelled is $10 S$, then ratio $\frac{S}{t^2}$ is
$\frac{2 \beta}{19}$
$\frac{2 \beta}{49}$
$\frac{\beta}{49}$
$\frac{2 \beta}{64}$
A glass slab of 16 cm thickness has its bottom surface silvered. An air bubble is located inside the glass slab at a distance of 8 cm from the top surface. The refractive index of glass is 1.6 . Which of the following correctly represents the number of images seen by an observer looking vertically downwards from air onto the top surface?
A. Only one image is seen at a depth of 5 cm
B. Multiple images are formed due to multiple reflections and refractions
C. Only one image is seen at a depth of 16 cm
D. Two images are seen at depths 5 cm and 15 cm
B
C
D
A
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