The point of this question is to compare rest energy and kinetic energy at low speeds. A baseball is moving at a speed of 12 m/s. Its mass is 145 grams (0.145 kg).

a. What is its rest energy?
b. Calculate its kinetic energy using the formula
c. What is its kinetic energy?
d. Which is true?

1. The kinetic energy is much bigger than the rest energy.
2. The kinetic energy is approximately equal to the rest energy.
3. The kinetic energy is much smaller than the rest energy.

Erest = m×

        = 0.145kg × 3×

        = 1.305× J

b) finding the kinetic energy

Ek = 0.5×0.145×

    = 1.044×J

c) the kinetic energy is smaller than rest energy

d) number 3 is true                                                                                                                                            

Explanation:

powerful computers now, not then

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