A football of radius $R$ is kept on a hole of radius $r (r < R)$ made on a plank kept horizontally. One end of the plank is now lifted so that it gets tilted making an angle $\theta$ from the horizontal as shown in the figure below. The maximum value of $\theta$ so that the football does not start rolling down the plank satisfies (figure is schematic and not drawn to scale) -
$\sin \theta=\frac{r}{R}$
$\tan \theta=\frac{r}{R}$
$\sin \theta=\frac{r}{2 R}$
$\cos \theta=\frac{r}{2 R}$
Write Aristotle’s law regarding motion.
$A$ flexible chain of weight $W$ hangs between two fixed points $A$ & $B$ which are at he same horizontal level. The inclination of the chain with the horizontal at both the points of support is $\theta$ . What is the tension of the chain at the mid point?
Give the magnitude and direction of the net force acting on a stone of mass $0.1\; kg$,
$(a)$ just after it is dropped from the window of a stationary train,
$(b)$ just after it is dropped from the window of a train running at a constant velocity of $36 \;km/h$,
$(c)$ just after it is dropped from the window of a train accelerating with $1\; m s^{-2}$,
$(d)$ lying on the floor of a train which is accelerating with $1\; m s^{-2}$, the stone being at rest relative to the train.
Neglect air resistance throughout.
A car accelerates on a horizontal road due to the forces exerted by
What was mistake in Aristotle’s idea regarding motion ?