Question

a body covers 12m in 2nd second and 20 m in 4th second. the distance the body will be covered in first 4th second is

Answer 1

s2=u+a/2(2n-1)
12=u+a/2(2*2-1)
12=u+a/2*(3)
12=(2u+3a)/2
2u+3a=24.......(a)

s4=u+a/2(2*4-1)
20 =u+a/2*(7)=u+7a/2
20=(2u+7a)/2
2u+7a=40.......(b)
equation (b)-(a),
2u+7a=40
2u+3a=24
- - -
so,4a=16
a=4m/s^2
putting the value of a in equation (a),we get
2u+3(4)=24
u=(24-12)/2=6m/s
distance covered in first 4 seconds=
s=ut+1/2at^2
s=6*4+1/2*4*4*4
=24+64/2=24+32
s=56m