A girl holds a book of mass $m$ against a vertical wall with a horizontal force $F$ using her finger, so that the book does not move. The frictional force on the book by the wall is
$F$ and along the finger but pointing towards the girl
$\mu F$ upwards, where $\mu$ is the coefficient of static friction
$m g$ and upwards
equal and opposite to the resultant of $F$ and $m g$
A body of weight $50 \,N$ placed on a horizontal surface is just moved by a force of $28.2\, N$. The frictional force and the normal reaction are
A block of mass $m$ (initially at rest) is sliding up (in vertical direction) against a rough vertical wall with the help of a force $F$ whose magnitude is constant but direction is changing. $\theta = {\theta _0}t$ where $t$ is time in sec. At $t$ = $0$ , the force is in vertical upward direction and then as time passes its direction is getting along normal, i.e., $\theta = \frac{\pi }{2}$ .The value of $F$ so that the block comes to rest when $\theta = \frac{\pi }{2}$ , is
An isolated rail car originally moving with speed $v_0$ on a straight, frictionles, level track contains a large amount of sand. $A$ release valve on the bottom of the car malfunctions, and sand begins to pour out straight down relative to the rail car. What happens to the speed of the rail car as the sand pours out?
A block of mass $M$ is being pulled along rough horizontal surface. The coefficient of friction between the block and the surface is $\mu $. If another block of mass $M/2$ is placed on the block and it is again pulled on the surface, the coefficient of friction between the block and the surface will be
Imagine the situation in which the given arrangement is placed inside a trolley that can move only in the horizontal direction, as shown in figure. If the trolley is accelerated horizontally along the positive $x$ -axis with $a_0$, then Identify the correct statement $(s)$ related to the tension $T$ in the string