Question

Push a pebble lying on a surface. The pebble moves through a distance. You exerted a force on the pebble and the pebble got displaced. In this situation work is done. A girl pulls a trolley and the trolley moves through a distance. The girl has exerted a force on the trolley and it is displaced. Therefore, work is done. Lift a book through a height. To do this you must apply a force. The book rises up. There is a force applied on the book and the book has moved. Hence, work is done. A closer look at the above situations reveals that two conditions need to be satisfied for work to be done: (i) a force should act on an object, and (ii) the object must be displaced.(a) Can work done by external force on an object be negative? (b) Write the SI unit of energy.(c) Write two conditions needs to be satisfied for work. (d) Define power.

Answer 1

Answer:

1. a force should act on a object.
2. When work is done by external forces (nonconservative forces), the total mechanical energy of the object is altered. The work that is done can be positive work or negative work depending on whether the force doing the work is directed opposite the object's motion or in the same direction as the object's motion.
3. joule
4. 1. For work to be done , the force must be applied and must not be zero. 2. work is done when the object moves through a certain distance in a particular direction after the force had been applied on it.
5. In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one joule per second. In older works, power is sometimes called activity. Power is a scalar quantity.

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Answer 2

a) Yes, it can be negative

b) Joule

c) (i) a force should act on an object, and (ii) the object must be displaced

d) power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one joule per second. In older works, power is sometimes called activity. Power is a scalar quantity.

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