Which of these does not result in the acceleration of an object?
a.) a decrease in speed
b.) an increase in speed
c.) a change in direction
d.) maintaining a constant velocity

I guess the correct answer is the first one.

The correct answer is D.

Acceleration is defined as a change in velocity. A and B clearly demonstrate a change in velocity so are eliminated. And since velocity is a vector quantity that consists of both magnitude and direction, C is also eliminated because it has a change in direction.

Let me know if you have any questions.

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