If a particle is moving on a circular path with constant speed, then the angle between the direction of acceleration and its position vector w.r.t. centre of circle will be ............ 

A car is moving in a circular horizontal track of radius $10\, m$ with a constant speed of $10 \,m/sec$. A plumb bob is suspended from the roof of the car by a light rigid rod of length $1.00\, m$. The angle made by the rod with track is ........ $^o$

An electron is moving in a circle of radius $2 \,m$ with speed $4 \,m / s$ Find the acceleration of the electron. (in $m / s ^{2}$)

A man standing on the roof of a house of height $h$ throws one particle vertically downwards and another particle horizontally with the same velocity $u$. The ratio of their velocities when they reach the earth's surface will be

The driver of a car travelling at velocity $v$ suddenly see a broad wall in front of him at a distance $d$. He should

Can you associate vectors with $(a)$ the length of a wire bent into a loop, $(b)$ a plane area, $(c)$ a sphere ? Explain.