Squares and Square Roots & Cubes and Cube Roots - Exercise

NCERT Exemplar Solutions Class 8 Mathematics Solutions for Squares and Square Roots & Cubes and Cube Roots - Exercise in Chapter 3 - Squares and Square Roots & Cubes and Cube Roots

Question 81 Squares and Square Roots & Cubes and Cube Roots - Exercise

999 is a perfect cube.

Answer:

False.

Video transcript

hello students welcome to leader learning's question and answer videos my name is pallabi and i teach math and science at lido let's have a look at this very interesting question in front of us so we have to write true or false for each statement wow that seems simple isn't it okay so the first statement is that a pulley does no work against force of gravity while carrying a luggage on the road so let's say this is the road and this is our so this is our kohli and he is carrying a luggage on his head right if the cooley was lifting the luggage then it would have been in the direction of the force right that is the force of the the force is what the force is the weight the combined weight of cooli and his luggage but in this case he is not lifting it he is in fact moving on the road so the direction of motion is perpendicular to the direction of the force so the displacement is perpendicular to the direction of the force when that happens work done is zero so therefore cooley does no work against the force of gravity while carrying luggage on a road this part is true okay let's move ahead to the next case so the next case says the energy stored in water of a dam is called is the kinetic energy so kinetic energy we know that kinetic energy is the energy of the body due to its motion so energy due to motion is kinetic energy now let's just see what is happening here so a dam as we know is at a height right let's say that is h and over here we have a water reservoir that is this reservoir contains water so the water is stored over here that is not moving therefore it cannot have any kinetic energy here but yes the what has some energy what is that called yes the water water has potential energy so over here the answer for this will be false because the energy stored is not kinetic energy but it is potential energy okay let's go ahead and talk about the next one so energy of a flying kite is kinetic energy now we talked we talked about this that is whenever an object is in motion the energy possessed by the object is called kinetic energy therefore the flying kite is a kite which is in motion so kite is in motion therefore the energy possessed by it will be scientific energy therefore this is true let's move ahead to the next one work done by boy depends on the time in which he does work so let's talk about work done now work done is given as force which is applied multiplied by the distance or displacement of the object so if an object is moved let's say this is a box if this is moved from here to here then work is done it does not depend on the time as you can see from the formula itself nowhere the time option is there right there is no time unit here it's force and distance it depends on two quantities force and distance therefore the answer to this will be false because it does not depend on the type however now let's move ahead and talk about the last part that is power spent by a body depends on the time for which it does work so let's talk about power power is the rate of doing work now rate of doing work means how fast an object or body or a person is doing work therefore work done upon time is power now we know that the factor of time has come here therefore the power spent by a body will depend on the time for which it is doing work therefore this will be true i hope you understood this if you have any further questions please post your comments below thank you

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