In a hydrogen atom, the distance between the electron and proton is $2.5 \times {10^{ - 11}}\,m$. The electrical force of attraction between them will be
$2.8 \times {10^{ - 7}}\,N$
$3.7 \times {10^{ - 7}}N$
$6.2 \times {10^{ - 7}}N$
$9.1 \times {10^{ - 7}}N$
In the figure shown, $A$ & $B$ are free to move. All the surfaces are smooth. then $(0 < \theta < 90^o)$
A boy is hanging from branch of a tree as shown. Angle between his arm, for tension to be maximum in arms must be ............ $^o$
For given systen ${\theta _1}$ ....... $^o$
At the instant $t = 0$ a force $F = kt$ ( $k$ is a constant) acts on a small body of mass $m$ resting on a smooth horizontal surface. The time, when body leaves the surface is