KVPY SA Exam 2015 Question Paper

Question : 21 of 80

Marks: +1, -0

A parachutist with total weight 75 kg drops vertically onto a sandy ground with a speed of 2 ms

^{-1}

and comes to a halt over a distance of 0.25 m. The average force from the ground on her is close to

Solution:

∆K.E. = 0 -1/ 2 mv^ 2

∆K.E. =-1/2 75(2)^2

∆K.E. =- 150 J

Total work done by forces = – 150 J

- F. ∆x = -150 J

F=150/{∆x}

(avg force)

F=150/0.25⇒F=600

N (upward direction)

F_R - mg = F

F_R = F + mg

F_R = 600 + 750

F_R = 1350 N

(resistive force by ground)

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