A 96lb boy is standing in an elevator. Find the force on the boy's feet when the elevator(a)stands still(b)moves downward at a constant velocity of 3 ft/d(c)accelerates downward with an acceleration of 4.0 ft/s2, and(d)accelerates upward with an acceleration of 4.0ft/s2

Explanation:

a ) When the elevator is at rest

R = mg

R =  force on the boy's feet = 96 x 32

= 3072 unit .

b ) When the elevator moves with uniform velocity , net force on the boy = 0

R = mg

force on the boy's feet = 96 x 32

= 3072 unit

c ) When the elevator moves with acceleration a  downwards

Reaction force R = mg - ma

= m ( g-a )

= 96 ( 9.8 - 4 )

= 556.8 unit

d )

When the elevator moves with acceleration a  upwards

Reaction force R = mg + ma

= m ( g+a )

= 96 ( 9.8 + 4 )

= 1324.8  poundal

the first american roller coaster was the mauch chunk switchback railway, built in the mountains of pennsylvania in the mid-1800s. the track, originally built to send coal to a railway, was reconfigured as a "scenic tour."

answer: at 24 february, 2014 the population gets twice of its initial population.

explanation:

since we have given that

the population for alpha city, t years after january 1, 2004 is given as

first we find out the initial population, i.e. t=0,

so, our quadratic equation becomes,

according to question, we have said that if the population has twice its initial population, then it becomes

so, time taken to reach this above mentioned population is given by

now, we know that time can't be negative so, we take t=9.149 years.

hence, at 24 february, 2014 the population gets twice of its initial population.