Question

A body travels 200 cm in first two sec. and 220 in the next 4 sec. what will be the velocity at the end of 7 sec. from start

Answer 1

formula to be used
$s = ut + \frac{1}{2}a {t}^{2}$
displacement in first two seconds =200 cm=2 m where s is displacement, u is initial velocity and v is final velocity , a is acceleration . time =2 seconds.
$2 = u(2) + \frac{1}{2}a {(2)}^{2}$
=>
$2 = 2u + 2a = > 1 = u + a...(1)$
displacement covered in 6 seconds=2+2.2=4.2 ,
time =6 seconds .
=>
$4.2 = u(6) + \frac{1}{2}a {(6)}^{2}$
=>
$4.2 = 6u + 18a = > 1.4 = u + 3a..(2)$
subtract (1) from (2)=> 2a=0.4 => a=0.2 ms^-2 . Substitute a=0.2 in equation (1)=> 1=0.2 +u =>
u=0.8 m/s . So to find velocity after 7 seconds , use
v=u+at => v=0.8+0.2(7) =0.8+1.4 =2.2m/s . 2.2 metre per second is the velocity after 7 seconds . Hope it helps you...