Use Newton's laws to explain why a falling object dropped from a 57m tower accelerates initially but then reaches constant veloc
1 answer:
Answer:
At the point of dropping the object, by Newton's first law due to gravitational force = m × g, accelerates
By Newton's Second law the object reaches impacts on the air with the gravitational force resulting in changing momentum of m×(Final Velocity - Initial Velocity)
As the velocity increases, the rate of change of momentum becomes equivalent to the gravitational force and by Newton's third law, the action action and reaction are equal and opposite hence they cancel each other out
The body then moves at a constant uniform motion down according to Newton's first law
Explanation:
At the point the object of mass, m, is dropped from the height of the tower, the only force acting on the object is the gravitational force such that the object has an acceleration which is the acceleration due to gravity, g, and the gravitational force is therefore = m × g
As the speed of the object increases while the object is falling with the gravitational acceleration the rate at which the object cuts through layers of air which (by Newton's first law of motion, are at rest ) has some buoyancy effect also increases therefore, the object is constantly increasingly changing the momentum of the air which by Newton's second law results, at an high enough velocity, and by Newton's third law, in a force equal to the applied gravitational force
Therefore, the force of the air drag becomes equal to the gravitational force, cancelling each other out and the object then moves according to Newton;s first law, in uniform motion of a constant speed while still falling down.
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17.
There are three different methods for charging objects:
- Friction: in friction, two objects are rubbed against each other. As a result, electrons can be passed from one object to the other, so one object will gain a net negative charge while the other object will gain a net positive charge due to the lack of electrons.
- Conduction: this occurs when two conductive objects are put in contact with each other, and charges (electrons, usually) are transferred from one object to the other one.
- Induction: this occurs when two objects are brought closer to each other, but not in contact. If one of the two objects has a net charge (different from zero) on its surface, then it will induce a movement of charges in the second object: in particular, in the second object, charges of the opposite polarity will be attracted towards the first object, while charges of same polarity will be repelled further away.
18.
Charged objects produce around themselves an electric field. The strenght of the electric field is given by (assuming the charged objects are spherical)
where k is the Coulomb's constant, q is the magnitude of the charge and r the distance from the centre of the charge. As we see, the strength of the field is inversely proportional to the square of the distance.
Also, the direction of the field is determined by the sign of the charge:
- if the charge is positive, the electric field points away from the charge (this means that other positive charges in the field will be repelled away)
- if the charge is negative, the electric field points towards the charge (this means that other positive charges in the field will be attracted towards it)
19.
Electrical force is given by:
where k is the Coulomb's constant, q1 and q2 are the two charges, and r their separation.
Gravitational force is given by:
where G is the gravitational constant, m1 and m2 are the masses of the two objects, and r their separation.
Similarities between the two forces:
- Both are inversely proportional to the square of the distance between the two objects, r
- Both are non-contact forces (the two objects can experience the forces even if they are not in contact)
- Both forces have infinite range
Differencies between the two forces:
- The electric force can be either attractive or repulsive, while the gravitational force is attractive only
- The electric force is much stronger than the gravitational force, due to the much larger value of the Coulomb's constant k compared to the gravitational constant G