Some of these frictions depend on the Pressure, temperature of atmosphere.
Static Friction: This is the friction force when two objects in contact are not moving relative to each other. This friction is higher than kinetic friction.
Kinetic or Dynamic friction: this the friction force opposing the motion of objects, when two objects in contact are in motion relative to each other. It is less than the static friction. The two surfaces are rubbing against each other as they move.
Rolling friction: This is the friction when two objects are in contact and one object is rolling over the other - like a wheel on a road. The point of contact appears as stationary. The rolling friction is very less compared to static friction & dynamic friction.
Lubricated friction: this is the friction between two solid surfaces in contact with a layer of lubricant fluid flowing in between them. This friction is the least.
Fluid friction - viscosity : this is friction between two adjacent layers that are moving relative to each other at different speeds in a fluid. This is not high.
Internal friction: when an object is compressed and forced to deform, like in a piece of rubber, there is friction between the layers, that opposes this deformation.
Skin friction is the friction that opposes movement of a fluid across a solid surface. This is also called drag. When a coin is dropped in water, there is a friction called drag on the coin. Same is the case when a ball is thrown, a drag is experienced by the ball due to the drag of air.
Answer:
When the bag of apples are on the floor, the force of gravity is equal to the force applied in the upward direction.
But when the girl picks up the bag of apples, she applies a force on the bag of apples in the upward direction greater than that of the gravitational force.
Explanation:
Gravitational force for an object is always constant at a specific point. When an object is in the state of rest, there is an equal force opposite to the direction of Gravitational Force.
Now, to lift an object upwards, an external force must be applied that is greater than the force of gravitation.
So, when the girl picks up the bag of apples,
Gravitational Force < Force applied by the girl to lift the bag.
Kinetic energy = momentum^2 / 2 x mass
Mass = (momentum^2/ Kinetic energy) / 2
Mass = (25^2 / 275) / 2
Mass = 1.136 kg.
momentum = mass x velocity
velocity = mass / momentum
velocity = 1.136 / 25
velocity = 0.04544 m/s
Answer:
(c) position
Explanation:
From the work-energy theorem, the workdone by a force on a body causes a change in kinetic energy of the body.
But, remember that the work done (W) by a force (F) on a body is the product of the force and the distance d, moved by the body caused by the force. i.e
W = F x d
This distance is a measure of the position of the body at a given instance.
Therefore, the work done is given by the force as a function of distance (or position).
