Which of the following is true?
a. the earth exerts a gravitational force on the moon, but the moon does not exert a gravitational force on the earth.
b. the earth and moon both exert a gravitational force on each other.
c. the moon exerts a gravitational force on the earth, but the earth does not exert a gravitational force on the moon.
d. the earth and moon do not exert gravitational forces.

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

3. dark matter

empty space could also be a simple vacuum