Physics [2 Mark Question Answer]

A planet moves around the sun in a nearly circular path for which the gravitational force of attraction on the planet by the sun provides the necessary centripetal force required for circular motion.

When a particle moves with a constant speed in a circular path, its motion is said to be the uniform circular motion. For example Revolution of earth around the sun is an example of uniform circular motion.

(a) On standing outside the disc, we find that the pebble is moving on a circular path.
(b) On standing at the centre of the disc, we find that the pebble is stationary placed just in front of us.

The position of the centre of gravity of a body of given mass depends on its shape i.e., on the distribution of mass in it. For example, the centre of gravity of a uniform wire is at its mid-point. But if this wire is bent into the form of a circle, its centre of gravity will then be at the centre of the circle.

Centre of gravity is the point about which the algebraic sum of moments of weights of particles constituting the body is zero and the entire weight of the body is considered to act at this point.

Length r = 10 cm = 0.1 m

F = 5N

Moment of force = F x r = 5 x 0.1 = 0.5 Nm

Moment of force = force x perpendicular distance of from point O

Moment of force = F x r

5Nm = 10 x r

R = 5/10 = 0.5 m

Anticlockwise moment if mass m is moved to the mark 10 cm= 50 g x (40-10) cm = 50 x 30=1500g cm

Clockwise moment=100g x (50 - 40) cm= 1000 g cm

Resultant moment= 1500 g cm -1000 g cm= 500 g cm (anticlockwise)

From the principle of moments

Clockwise moment = Anticlockwise moment

100g x (50 - 40) cm = m x (40 - 20) cm

100g x 10 cm = m x 20 cm = m = 50 g

Anticlockwise moment = 10 gf x 50 cm = 500 gf cm

Moment of a force is the product of the force and the perpendicular distance of force from axis of rotation. So, one way to increase the moment would be to increase the distance from the axis of rotation where the force would act.

Moment of force depends on the distance of the line of action of the force from the axis of rotation. Decreasing the perpendicular distance from the axis reduces the moment of a given force.

If the turning effect on the body is anticlockwise, the moment of force is called anticlockwise moment and it is taken as positive while if the turning effect on the body is clockwise, the moment of force is called clockwise moment and is taken negative

Moment of force about a point depends on the following two factors:

(a) The magnitude of the force applied and,

(b) The distance of line of action of the force from the axis of rotation.

According to the principle of moments, if the algebraic sum of moments of all the forces acting on the body about the axis of rotation is zero, the body is in equilibrium. A physical balance (or beam balance) works on the principle of moments.

For a body to be in equilibrium:

1) The resultant of all the forces acting on the body should be equal to zero.

2) The resultant moment of all the forces acting on the body about the point of rotation should be zero.

When a body remains in the same state of motion (translational or rotational), under the influence of the applied forces the body is said to be in dynamic equilibrium. For example, a raindrop reaches the earth with a constant velocity is in dynamic equilibrium.

The moment of a couple is equal to the product of either force and the perpendicular distance between the line of action of both the forces. S.I unit of moment of the couple is Nm.

Resultant force acting on the body = F - F = 0

moment of forces = 0 i.e no motion of the body

It is easier to turn the steering wheel of a large diameter than that of a small diameter because less force is applied on the steering of large diameter which is at a large distance from the centre of the rim.