Question 732150
a particle sliding down an inclined plane travels 2 feet the first second. In any second after the first it slides 4 feet farther than it did in the preceding second. how far will it slide in 7th second? how far will it slide in 7 seconds? how long will it take to slide 128 feet?


t1=2 =a

t2=2+4=6

t3=6+4=10

a=2
d=4

tn= a+(n-1)d
t7=2+(7-1)4

t7= 26,  26 feet in the 7th. second

Sn=n/2[2a+(n-1)d]

S7=7/2[2*2+(7-1)4]

S7=7/2[28]

S7=98,   98 feet in 7 seconds


128=n/2[4+(n-1)2]

256=4n

256=4n +2n^2 -2n

2n^2+2n-256=0
/2
n^2+n-128=0
solve the quadratic for x

you will get n=10.82 

In 10.82 sec it will go 128 feet