Four charges equal to + Q are placed at the four corners of a square and a charge ($$-$$q) is at its centre. If the system is in equilibrium, then the value of $$-$$q is
A force F = a + bx acts on a particle in the x-direction where a and b are constants. The work done by this force during a displacement from x = 0 to x = d is
A proton has kinetic energy E = 100 eV which is equal to that of a photon. The wavelength of photon is $$\lambda$$2 and that of proton is $$\lambda$$1. The ratio $${{{\lambda _2}} \over {{\lambda _1}}}$$ is proportional to
A block of mass 10 kg rests on a rough inclined plane making an angle of 30$$^\circ$$ with the horizontal. The coefficient of static friction between the block and the plane is 0.1. The friction force on the block is