Explain how the gravitational force between the sun and earth changes as the earth moves from position A to B.

We all know that the sun revolves around the sun in the elliptical orbit which is oval in shape.
We also know that the gravitational force between different heavenly bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. In position 'A', the distance is shorter; so the gravitational force is higher but in position 'B', the distance is longer; so the gravitational force is less than that in position 'A'.

What stress would cause a wire to increase in length by one-tenth of one percent if the Young modulus for the wire is 12 × 1010 N/m2 ? What force would produce this stress if the diameter of the wi...

Solution:
The Young modulus of a wire, Y = 12 1010 N/m2 ;
the diameter of the wire, d = 0.56 mm = 0.56 10^–3 mm
The cross-section area of the wire,

The strain = one-tenth of 1 percent

Show that a hydraulic machine is a force multiplier.

Let us consider a hydraulic machine of 2 vessels of CSA 'A1' and 'A2' respectively. These vessels are fitted with watertight frictionless pistons. The CSA of the small vessel is 'A1' and large vessel is 'A2'. So, 'A1' < 'A2'.

When a force 'F1' is applied on the small piston of area 'A1', a pressure 'P1' is exerted on the small piston. According to Pascal's law:

Pressure in small piston = Pressure in the large piston
i. e. P1 = P2
or,    F1 / A1 = F2 / A2
or,    F1.A2 = F2.A1...

Why is tension called a pseudo force?

Torque and force are two different physical quantities, can they be added?

Torque has the dimension of force times distance, symbolically T²L²M. Although those fundamental dimensions are the same as that for energy or work, official SI literature suggests using the unit newton metre (Nm) and never the joule.

Why is a force necessary to keep a body moving with a uniform speed in a circular motion?

When a body is moving in a circle with uniform motion, its linear velocity will change continuously. Since the magnitude of the velocity does not change, the change in the velocity is due to the change in its direction. This change in velocity gives rise to a changing momentum. According to Newton's second law of motion, to bring any change in momentum, a force is required. Therefore centripetal force is required to keep the body in the circular motion.