Acceleration & Force: Lesser Force Impact on Mass

[pranav p v]

Consider a body of mass m at rest,then if I apply force f1 on that then it accelerates and attains a velocity of v1.then I remove that force..now the body is in uniform motion.if I apply a force f2 which is less than f1, then body will be accelerated or retardated?I know if same f1 is applied then acceleration will be the previous same value,and if I apply force greater than f1 then it will be accelerated ( but not uniform)..what about f2 less than f1

 

[phinds]

Consider a body of mass m at rest,then if I apply force f1 on that then it accelerates and attains a velocity of v1.then I remove that force..now the body is in uniform motion.if I apply a force f2 which is less than f1, then body will be accelerated or retardated?I know if same f1 is applied then acceleration will be the previous same value,and if I apply force greater than f1 then it will be accelerated ( but not uniform)..what about f2 less than f1

Well, if you applied f2 in a direction opposite that of the body's motion, then yes it would be retarded/decelerated.

 

[CWatters]

if I apply a force f₂ which is less than f₁, then body will be accelerated or retardated?

That depends on the direction of F₂.

I know if same f₁ is applied then acceleration will be the previous same value

Yes. If you apply F₁ again the acceleration will be the same a₂ = a₁.

if I apply force greater than f₁ then it will be accelerated ( but not uniform).

If you apply a force F₂ > F₁ the object will accelerate faster so a₂ > a₁. However if the new force is constant the new acceleration will also be constant (=uniform).

what about f₂ less than f₁

If F₂ < F₁ the new acceleration will be less than before, a₂ < a₁

All you need to remember is Newton's Law...
F = ma
so
a = F/m

The fact that the mass is moving does not change law.

 

[russ_watters]

F=ma, period. It doesn't remember previous action and doesn't know anything about speed.

 

[vanhees71]

Even more importantly $\vec{F}=m \vec{a}$, i.e., force and acceleration are both vectors!

 

[Lord Jestocost]

Consider a body of mass m at rest,then if I apply force f1 on that then it accelerates and attains a velocity of v1.then I remove that force..now the body is in uniform motion.if I apply a force f2 which is less than f1, then body will be accelerated or retardated?I know if same f1 is applied then acceleration will be the previous same value,and if I apply force greater than f1 then it will be accelerated ( but not uniform)..what about f2 less than f1

Start with the velocity equation in case of constant acceleration:

v(t) = v(t = t₀) + a⋅(t - t₀)

The body of mass m is moving with v₁ when you, at time t₂, suddenly apply a force f₂ to the body. The acceleration is then a = f₂/m. You get

v(t) = v(t = t₂) + f₂/m⋅(t - t₂) = v₁ + f₂/m⋅(t - t₂)