# Class 10th maths science group Chapter 3 Exercise 3.7

## Class 10th maths science group Chapter 3 Exercise 3.7

Class 10th maths science group Chapter 3 Exercise 3.710/26/2017 12:33:07 pm - notes - 10th - Mathematics Science Group - administrator
This series of lecture is about class 10th maths book exercise 3.7. You will get the lectures and notes about all the exercises of maths 9th, 10th, 11th, 12th. These lectures are related to Punjab Textbook Board PTB, Federal Board, Rawalpindi Board and all other educational boards of Punjab. 
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This Lecture includes complete notes of Exercise 3.7 Chapter 3 Variations from class 10th maths (science group) Punjab Text Book Board. For FBISE, RWPBISE and all other boards like Lahore Board, Sargodha Board etc.
In this Lecture you will go through following Topics:
1. Real life problems based on variation

Select a Question from the list bellow to see the video of that Question directly (works best in Google Chrome Browser):
Q. 1:	The surface area A of a cube varies directly as the square of the length l of an edge and A = 27 square units when l = 3 units.
Find 	(i) A when l = 4 units		(ii) l when A = 12 sq. units.
Q. 2:	The surface area S of a sphere varies directly as the square of radius r, and S = 16 pi when r = 2. Find r when S=36?.
Q. 3:	In Hook’s law the force F applied to stretch a spring varies directly as the amount of elongation S and
F=32lb when S=1.6 in. Find 	(i) S when F=50 lb		(ii) F when S=0.8in.
Q. 4:	The intensity I of light from a given source varies inversely as the square of the distance d from it. If the intensity is 20 candlepower at a distance of 12ft. from the source, find the intensity at a point 8ft. from the source.
Q. 5:	The pressure P in a body of fluid varies directly as the depth d. If the pressure exerted on the bottom of a tank by a column of fluid 5ft. high is 2.25 lb/sq. in, how deep must the fluid be to exert a pressure of 9 lb/sq. in?
Q. 6:	Labour costs c varies jointly as the number of workers n and the average number of days d, if the cost of 800 workers for 13 days is Rs. 286000, then find the labour cost of 600 workers for 18 days.
Q. 7:	The supporting load c of a pillar varies as the fourth power of its diameter d and inversely as the square of its length l. A pillar of diameter 6 inch and of height 30 feet will support a load of 63 tons. How high a 4 inch pillar must be to support a load of 28 tons?
Q. 8:	The time T required for an elevator to lift a weight varies jointly as the weight w and the lifting depth d varies inversely as the power p of the motor. If 25 sec. are required for a 4-hp motor to lift 500 lb through 40 ft, what power is required to lift 800 lb, through 120 ft in 40 sec.?
Q. 9:	The kinetic energy (K.E.) of a body varies jointly as the mass “m” of the body and the square of its velocity “v”. If the kinetic energy is 4320 ft/lb when the mass is 45 lb and the velocity is 24 ft/sec. Determine the kinetic energy of a 3000 lb automobile travelling 44 ft/sec.

Class 10th maths science group Chapter 3 Exercise 3.7 All exercises Full Solutions
Class 10th maths science group Chapter 3 Exercise 3.7 Notes
Class 10th maths science group Chapter 3 Exercise 3.7 Video lecture
Class 10th maths science group Chapter 3 Exercise 3.7 All Questions pdf Notes


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Maths Cheat Sheet

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