Physics Questions

without this centripetal force, circular motion is not possible. It acts radially towards the centre and if this force is removed there will be no circular motion but the revolving body will fly off at a tangent.

Black  surfaces are good emitters of heat ( They are also good absorbers of heat). If the black surface is rough too, the emitting will be better. So (b) is the correct answer. Shining surfaces reflect back radiation. So if the black surface is also shining the effectiveness of emitting heat is lessened.

When you compress or stretch a spring, as soon as the stress is relieved, the spring attains its normal shape instantly. Its Elastic potential energy helps it do so. Generally, these elastic substances follow the Hooke’s law.

According to this Law, the force needed to change the shape of spring is proportional to the displacement of the spring. The displacement referred here is how far the spring is compressed or stretched from its normal shape. Mathematically, Hook’s Law can be summarised as F= – k x. Here ‘k’ is the spring constant and ‘x’ is the displacement.

Electric current produces a magnetic field. This magnetic field can be visualized as a pattern of circular field lines surrounding a wire.

It is to overcome this opposite frictional force , that  we have to apply the needed force to make the body move

Every object has two typea of energies. They are ::

Potential energy

Kinetic energy

If the object is in motion, then it has Kinetic energy (KE). Potential energy (PE) is energy that is "stored" because of the position and/or arrangement of the object.

Hence, another name for energy of motion is called Kinetic energy.

1st copper wire: R = pl/A = pl/ πr2

2ndcopper wire: R’ = p’l’/A’ = pl/(4 πr2) = R/4

If joined in parallel, (1/Req) = (1/R) + (1/R’)

= 1/R + 4/R1/Req= 5/R

Req= R/5

Projectile