If vectors $$\overrightarrow A = \cos \omega t\widehat i + \sin \omega t\widehat j$$ and $$\overrightarrow B = \cos {{\omega t} \over 2}\widehat i + \sin {{\omega t} \over 2}\widehat j$$ are functions of time, then the value of t at which they are orthogonal to each other is

The positions vector of a particle $$\overrightarrow R $$ as a function of time is given by $$\overrightarrow R $$ = 4sin(2$$\pi $$t)$$\widehat i$$ + 4cos(2$$\pi $$t)$$\widehat j$$. Where R is in meters, t is in seconds and $$\widehat i$$ and $$\widehat j$$ denote unit vectors along x-and y-directions, respectively. Which one of the following statements is wrong for the motion of particle?

A ship A is moving Westwards with a speed of 10 km h^$$-$$1 and a ship B 100 km South of A, is moving Northwards with a speed of 10 km h^$$-$$1. The time after which the distance between them becomes shortest, is

A projectile is fired from the surface of the earth with a velocity of 5 m s^$$-$$1 and angle $$\theta $$ with the horizontal. Another projectile fired from another planet with a velocity of 3 m s^$$-$$1 at the same angle follows a trajectory which is identical with the trajectory of the projectile fired from the earth. The value of the acceleration due to gravity on the planet is (in m s^$$-$$2) is
(Given g = 9.8 m s^$$-$$2)