A person of mass 80 kg escapes from a burning building by jumping from a window situated 30 m above a catching net. The acceleration of grav

Question

A person of mass 80 kg escapes from a burning building by jumping from a window situated 30 m above a catching net. The acceleration of gravity is 9.8 m/s2 . If air friction exerts a constant force of 100 N on her as she falls, determine her speed just before she hits the net:_____
1. 24.6495 m/s
2. 22.9396 m/s
3. 6.37868 m/s
4. 17.4299 m/s

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Thông Đạt 2 days 2021-07-20T10:59:58+00:00 1 Answers 4 views 0

Answers ( )

    0
    2021-07-20T11:01:39+00:00

    Answer:

    Her speed just before she hits is 24.6495 m/s .

    Explanation:

    Given :

    Mass of person , m = 80 kg .

    Height from which it jumped , h = 30 m .

    acceleration of gravity is , g=9.8\ m/s^2 .

    Force exerted by air friction , f = 100 N .

    Now , force exerted by gravity is :

    F' = mg\\F'=80\times 9.8\\F'=784\ N

    Therefore , net force experience by the body is :

    F=F'-f\\F=784-100\ N\\F=684\ N

    Therefore , net acceleration of body is :

    a=\dfrac{F}{m}\\\\a=\dfrac{684}{80}\\\\a=8.55\ m/s^2

    So by equation of motion :

    v^2-u^2=2as\\\\v^2=2\times 8.55 \times 30\\\\v=22.6495\ m/s

    So , her speed just before she hits is 24.6495 m/s .

    Therefore , this is the required solution .

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