Why does a phonograph - record attract dust partiules just after it is cleaned?

A particle of mass m is kept on the top of a smooth sphere of radius R. It is given a sharp impulse which imparts it a horizontal speed v. a. find the normal force between the sphere and the particle just after the impulse. B. What should be the minimum value of v for which the particle does not slip on the sphere? c. Assuming the velocity v to be half the minimum calculated in part, d. find the angle made by the radius through the particle with the vertical when it leaves the sphere.

In the medium where E. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down some time after addition of lactose in the medium?

The earth revolves round the sun because the sun attracts the erth. The sun also attracts the moon and this force is about twice as large as the attraction of the earth on the mon. Why does the moon not revolve round the sun? Or does it?

i. Will the velocity of a stone thrown vertically upwards remian constant or will it change with time? How will it change? ii. Why doesn't the stone move up all the time? Why does it fall down after reaching a certain height? iii. What does its maximum height depend on?

A narrow slit S transmitting light of wavelength lamda is placed a distance d above a large plane mirror as shown in figure. The light coming directly from the slit and that coming after the reflection interference at a screen sum placed at a distance LD from the slit. a. What will be the intensity at a point just above the mirror. i.e., just above O? b. At what distance from O does the first maximum occur?

a. What happens if a bar magnet is cut into two pieces : (i) transverse to its length , (ii) along its length ? b. A magnetised needle in a uniform magnetic field experiences a torque but no net force . An iron nail near a bar magnet , however , experiences a force of attraction in addition to a torque . Why ? c. Must every magnetic configuration have a north pole and a south pole ? What about the field due to a toroid ? d. Two identical looking iron bars A and B are given , one of which is definitely known to be magnetised. (We do not know which one ) . How would one ascertain whether or not both are magnetised ? If only one is magnetised , how does one ascertain which one ? [Use nothing else but the bars A and B ]

Why does the zygote divides only after the division of Primary endosperm cells ?