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Home / Doubts and Solutions/JUNIOR/Class 10/Mathematics

  1. a girl of height 90cm is walking away from the base of a lamp post at a speed of 1.2 m/s . If the lamp is 3.6 m above the ground . Find the length of her shadoe after 4 sec

  1. the radius of the wheels of a bus is 70 cm . How many revolution per minute must a wheel make in order to move at a speed of 66 km/h?

  1. if -4 is a root of the quadratic equation x2 + px - 4 = 0and the quadratic equation x2 + px + k = 0 has equal roots. the value of k is

  1. a cylindrical water tank of diameter 1.4 m and height 2.1m is being fed by a pipe of diameter 3.5cm through which water flows at a rate of 2 m/sec. In how ​much time the tank will be filled

Asked by fasalikasu 25th March 2015, 6:34 PM
Answered by Expert
Answer:

HI Fasalikasu

 

begin mathsize 16px style Let space the space lamp space be space at space the space point space straight Q space space on space the space ground Height space of space the space lamp space equals space 3.6 space straight m space equals space 360 space cm space therefore PQ space equals space 360 space cm Let space the space girl space be space at space point space straight T Height space of space girl comma space ST equals space 90 space cm Let space the space length space of space the space shadow space equals straight x space cm Looking space at space the space figure space length space of space the space shadow space is space TR comma space therefore TR space equals space straight x The space girl space walks space at space the space speed space of space 1.2 space straight m divided by sec space equals space 120 space cm divided by sec therefore The space distance space travelled space by space the space girl space in space 4 space minutes space equals space 120 cross times 4 space equals space 480 space cm therefore The space distance space travelled space by space the space gir space equals QT space because increment PQR space tilde space increment STR comma therefore PQ over QR equals ST over TR space space space therefore fraction numerator PQ over denominator QT plus TR end fraction equals ST over TR space space space open parentheses because QR space equals space QT plus TR close parentheses therefore fraction numerator 360 over denominator 480 plus straight x end fraction equals 90 over straight x space space therefore 360 straight x space equals space 90 straight x plus open parentheses 480 cross times 90 close parentheses therefore 270 straight x equals 43200 comma space therefore straight x space equals space 160 space cm comma hence comma space length space of space the space shadow equals 160 space cm end style

Answered by Expert 25th March 2015, 7:25 PM
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