Question

an object of mass 1 kg moving alongx-axis with constant speed 8m/s,a constant force 2N is apllied in positive y-direction.Find its speed after 4 seconds

Answer 1

Vx = 8 { velocity in x - axis ) 
Fy = 2N { force act on body in y-direction } 

we know, 
F = ma 
2 = 1 × a 
a = 2 m/s² In y - direction , 

now, use vector kinematics formula 
V = U + at 
here, 
U = 8i 
a = 2j 
t = 4 

V = 8i + 2j × 4 = 8i + 8j 
hence, final velocity = 8i + 8j 
we know, speed = | velocity| 
speed = √(8² +8²) = √(2×8²) 
= 2√8 m/s 

Answer 2

F=m×v. (v=d/t)
2=1×d/t
2=d/4
d=8

speed= d/t
=8/4
=2m/sec

Hope it help