An objects thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object.
The amount of work done by the force of gravity on the object is zero. This is because the net displacement of the object is in the horizontal direction while the force of gravity acts in the vertical downward direction.
A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.
We have,
Mass m kept on table, m = 10 kg
Displacement of mass from A to B is horizontal.
Force of gravitation acts vertically downwards. That is, force acts perpendicular to displacement.
∴ W = Fs cos 90° = 0.
Work done on the object by the gravitaional force is 0.
A battery lights a bulb. Describe the energy changes involved in the process.
When a battery lights a bulb, first the battery converts chemical energy into electrical energy. This electrical energy is converted into heat and light.
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
No, the law of conservation of energy is not violated. The loss in potential energy appears as an equal gain in kinetic energy of the object. Hence, the law of conservation of energy remains conserved.
Certain force acting on a 20 kg mass changes its velocity from 5 ms-1 to 2 ms-1. Calculate the work done by the force.
Given,
Mass, m = 20 kg
Initial velocity, u= 5 ms-1
Final velocity, v= 2 ms-1
Work done = change in K. E.
W = mv2 - mu2
= m ( v2 - u2)
= x 20 x (22 - 52)
= 10 (4-25)
= -10 x 21
= -210 J
Here, the negative sign implies the retarding nature of the applied force.
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