Which of the following statements are true?
(a) an object can move even when no force acts on it.

(b) if an object isn't moving, no external forces act on it.

(c) if a single force acts on an object, the object accelerates.

(d) if an object accelerates, a force is acting on it.

(e) if an object isn't accelerating, no external force is acting on it.

(f) if the net force acting on an object is in the positive x-direction, the object moves only in the positive x-direction.

Statements A, C, D, and E are all true.

Statements B and F are false.

no. dot product   =0 when vecs at right angles

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