Question

On an object of mass 1 kg moving along x axis with const speed v =8 m/s a const force 2 n is applied in positive y direction find speed after 4 sec

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

Vx = 8 
Fy = 2N 
It is known to us that,
F = ma 
2 = 1 × a 
a = 2 m/s² In y - direction , 
by using vector kinematic formula we'll get
V = U + at 
Given Here
U = 8i 
a = 2j 
t = 4 
V = 8i + 2j × 4 = 8i + 8j 
⇒ Final velocity = 8i + 8j 
Speed = | velocity| 
Speed = √(8² +8²)
           = √(2×8²) 
            = 2√8 m/s