Question

(i) When do you say that an object has positive acceleration? (ii) When do you say that an object has negative acceleration?​

Answer 1

EXPLANATION :-

Firstly lets know about acceleration :-

Acceleration :- Acceleration is defined as change in velocity per unit time is called acceleration .

Acceleration = Change in velocity / time

Acceleration = Final velocity - Initial velocity / time

a = v -u /t

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Now ,

Acceleration can be positive or negative .

When do we say that acceleration is positive ?

A) When the body is speeding up i.e increasing the speed and moves in same direction then acceleration is positive .

Increasing speed means i.e it is positive. and time is always positive

So,

a = +ve /+ ve

a = positive

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When do we say that acceleration is negative ?

A) When the speed of the body is decreasing and moves in opposite direction it will have negative acceleration .

Decreasing the speed means it speed gradually decreases and  can come in negative also So , here speed is negative and time is positive

So,

a = -ve /+ ve

a = negative

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Answer 2

Explanation:

The bacteria colonize plant cells within root nodules, where they convert atmospheric nitrogen into ammonia using the enzyme nitrogenase and then provide organic nitrogenous compounds such as glutamine or ureides to the plant. The plant, in turn, provides the bacteria with organic compounds made by photosynthesis. This mutually beneficial relationship is true of all of the rhizobia, of which the genus Rhizobium is a typical example. Rhizobium is also capable to solubilize phosphorus.