According to newton’s second law of motion, an object will accelerate if you apply what kind of force?

a. inertial force

b. frictional force

c. balanced force

d. unbalanced force

From Newton's first law of motion we know that every body continues to be at sate of rest or of uniform motion along a straight line unless and until it is compelled by some external unbalanced force.

It is the unbalanced which creates acceleration in a body.

Newton's second law gives the quantitative definition of force which tells that the net external unbalanced force is the product of mass with acceleration.

Mathematically force = mass×acceleration

                            ⇒   F  = ma

Force is a vector quantity.There might be many forces acting on a body at different directions,but they can not produce any acceleration.Several forces may cancel each other. Only the resultant force is responsible for the acceleration of the body.

Hence the correct answer to this question is D.unbalanced force

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s