In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.
Work is done whenever the given conditions are satisfied:
(i) Force is applied.
(ii) Displacement takes place.
(iii) The angle between the force and displacement is not 90 degrees .
Case I
In this case, the angle between the force and displacement is 90 degrees. Hence, work done by force on the block will be zero.
Case II
In this case, the angle between the force and displacement is 0 degree. Hence, work done by force on the block will be positive.
Case III
In this case, the angle between the force and displacement is 180 degrees. Hence, work done by force on the block will be negative.
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
A freely falling object eventually stops on reaching the ground. What happenes to its kinetic energy?
Define 1 J of work.
Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?
The kinetic energy of an object of mass, m moving with a velocity of 5 m s-1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Certain force acting on a 20 kg mass changes its velocity from 5 m s-1 to 2 m s-1. Calculate the work done by the force.
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
State the universal law of gravitation.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
What is meant by a pure substance?
How does the sound produced by a vibrating object in a medium reach your ear?
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
What are canal rays?
State any two conditions essential for good health.
How is our atmosphere different from the atmospheres on Venus and Mars?
Who discovered cells, and how?
How is a prokaryotic cell different from a eukaryotic cell?
Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Explain how bats use ultrasound to catch a prey.
How do good animal husbandry practices benefit farmers?
How do storage grain losses occur?
To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K. Find its concentration at this temperature.
For the symbol H,D and T tabulate three sub-atomic particles found in each of them.
Which one of the following is a correct electronic configuration of sodium?
(a) 2,8 (b) 8,2,1 (c) 2,1,8 (d) 2,8,1.
Why should preventive measures and biological control methods be preferred for protecting crops?
If K and L shells of an atom are full, then what would be the total number of electrons in the atom?