  Selina solutions

# Question 12

Q12) It takes 20s for a girl A to climb up the stairs while girl B takes 15 s for the same job.

(a) Compare the work done.

(b) Compare the power spent by then.

• Solution

• Transcript

Solution:

(a) As height is same for both girls A and B, work done is same

Work done by A : Work done by B = 1 : 1

(b) Power = Energy/Time

= 15 : 20

= 3 : 4

Hello students, welcome to Lido Learning's question-and-answer videos my name is pallabi and I teach maths and science at lido Let's have a look at this very interesting question so it takes around 20 seconds for girl and let's say this is a girl and to climb up the stairs while girl b let's say this is girl b she is taking 15 seconds so she takes Less time than girl a right who takes 20 seconds to do the same job so we have to calculate two things over here is compare the work done so how much work is done by both of them who are doing more work and the second thing is to compare the power spent by them that is who is having more power or who is spending more power right okay so before we calculate the power Let's start with the first part which is work done so we know that the work done is in the force into displacement so in this case if you see observe carefully both girls a and b are moving the same staircase right they are climbing up the stairs that is the same staircase so the displacement at the end is the same for both of them so displacement is the same therefore and the force is also the same because the The girls are identical, let's say, therefore. Work Done is the same so we may say let's consider that as w so w is the work done by both a and b right okay so compare the work done so let's say it is same okay let's move ahead to the next the part which compares the power spent by them so before we go ahead with this Let's just define power. the power of a body is defined as the rate of doing work or work done upon the time taken that will give us the path or energy upon time si unit of power is joules per second which is also called what so let's calculate the powers in in this case so let's say the power for the first the girl is par one r1 is how much work is done which is w upon time is taken by the first girl here it is 20 right so w by 20 becomes p1 for the second girl, let's say the power is p2 which is again work done which is again w upon the time taken which is 15 in this case because she takes less time right now to compare these two what do we do we just divide one with two so we get power one upon power 2 is equal to w by 20 divided by w by 3 so we may write it as 15 by w multiplied by these two gettings canceled so 3 5 5 3's and 5 4 so we get power 1 upon power 2 is equal to 3 upon 4 or power 1 is to power 2 is equal to 3 is to 4 I hope this point was clear so the Second Girl has more power because as you see the ratio according to the ratio of the second Girls have more power right now, I hope this point was clear if you have any further questions please post your comments below, thank you

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