Question

The potential energy of a catapult was completely converted into kinetic energy by releasing a small stone with a mass of 20 grams. The velocity of the stone when it reached the target was 15.0 meters/second. What was the value of the kinetic energy of the stone when it reached the target? A. 2.05 joules B. 2.25 joules C. 3.20 joules D. 4.43 joules

Answer 1

Answer : The correct option is, 2.25 joules.

Explanation : Given,

Mass of the stone = 20 g

Velocity of the stone = 15 m/s

Formula used for kinetic energy is :

$K.E=\frac{1}{2}mv^2$

where,

K.E = kinetic energy of the stone

m = mass of the stone

v = velocity of the stone

Now put all the given values in this formula, we get the kinetic energy of the stone.

$K.E=\frac{1}{2}\times (20g)\times (15m/s)^2$

$K.E=2250gm^2/s^2=2.25Kgm^2/s^2=2.25J$

Therefore, The kinetic energy of the stone is, 2.25 joules.

Answer 2

1,000 grams = 1 kilogram

20 grams = 0.02 kilogram

Kinetic energy = (1/2) (mass) x (speed)²

                          (1/2) (0.02) x (15)² =

                                (0.01)  x  (225)  =  2.25 joules