What is the sum of the forces in an action reaction pair?
o a.
always less than zero
b.
always greater than zero
c.
always equal to zero
sometimes less than zero
reset

C.  always equal to zero

Explanation:

According to newton's third law of motion, every action is always associated with equal and opposite reactions.

If object A applies a force to object B, then object B imparts a force equal to that of A towards it. So, the direction of force is opposite to each other.

The action force is called 'Fa' and the reaction force is '-Fr'

Due to the reversal of direction, the magnitude of the reaction force has a negative sign.

                                           Fa = - Fr

∴                                          Fa  +  (-Fr) = 0

Hence, sum of these two forces is equal to zero.

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