Question

A body covers 12m in 2nd second and 20m in 4th second. How much distance will it cover in 4 seconds after the 5th

second?​

Answer 1

Answer:

136 m of distance it will cover in 4 seconds after the 5th second.

Answer 2

Answer:

136 m

Explanation:

Sn = u + a/2 ( 2n - 1)

A body covers 12m in the 2nd second ( given)

s2 = 12

12 = u + a/2 ( 2 × 2 - 1)

12 = u + 3a/2 --------(1)

and

In 4th second it's cover 20m

s4 = 20

20 = u + a/2 ( 2 × 4 -1)

20 = u + 7a/2 -----(2)

substracting Eq (1)&(2)--

u + 3a/2 = 12

u + 7a/2 = 20

(-) (-) (-)

____________

3a/2 - 7a/2 = -8

(3a-7a)/2 = -8

-4a/2 = -8

a = 4m/s

from eq (1) ----

12 = u + 3a/2

put the value of 'a' ------

12= u + 12/2

u = 6m/s

Now,

Distance covered in 4th second after the 5th second

= s9 - S5

= u(9) + a(9)²/2 - [ u(4) + a(5)²/2]

= 9u + 81a/2 - [ 5u + 25a/2 ]

= 9u + 81a/2 - 5u - 25a/2

= 4u + a/2( 81-25)

put the value of 'u' and 'a'-----

= 4×6 + 4/2× 56

= 24 + 4 × 28

= 136m