A3.0kg mass is held 4.2 m above the ground. what is the potential energy of the mass with respect to the ground?

126 joules

Potential energy is the energy possessed by a body while at rest.

It is calculated by the formula m×g×h; where m is the mass, h is the height and g is the gravitational acceleration, 10N/kg

Potential energy = m×g×h

                           = 3.0 × 4.2 × 10

                           =  126 joules

d. air pressure decreases as altitude increases.

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