Physics Question & Answer Key

Question 1:

A 75 kg person escapes from a burning building by walking out a window 25m above a catching net. Assuming that air resistance is a constant 95N on the person during the fall, calculate the person's velocity just before hitting the net.

F = ma

(75)(9.8) - 95  = 75a

a = 8.53 

s = (1/2)(a)(t^2)

25 = (1/2)(8.53)(t^2)

t = 2.42

 v = u + (a)(t)
    = 0 + (8.5)(2.42)
    = 20.66 

 

Question 2:

The maximum force a grocery sack can withstand and not rip is 250 N. Calculate the greatest acceleration 20kg of groceries can be lifted from the floor to the table such that the sack does not break?

Fg = mg

     = (20)(9.8) = 196

F = ma

250 - 196 = (20)(a)

 a = 2.7