Question

A book falls off a desk. The book has a mass of 1.2 kg and was at a height of

0.9 m. How much mechanical energy does the book have just before it hits
the ground? (Assume there is no air resistance.)
A. 11.6 J
B. 15.4 J
C. 10.6 J
D. 7.7 J
SUBMIT

Answer 1

To calculate the mechanical energy of the book just before it hits the ground, we need to consider its potential energy and kinetic energy.

The potential energy (PE) of the book at a height of 0.9 m can be calculated using the formula: PE = mgh, where m is the mass of the book, g is the acceleration due to gravity, and h is the height.

Step-by-step explanation:

Given:

Mass of the book (m) = 1.2 kg

Height (h) = 0.9 m

Acceleration due to gravity (g) = 9.8 m/s^2 (approximate value on Earth)

Now we can calculate the potential energy:

PE = mgh

= 1.2 kg * 9.8 m/s^2 * 0.9 m

≈ 10.584 J

The mechanical energy just before the book hits the ground is equal to its potential energy, which is approximately 10.584 J.

Among the given options, the closest value to 10.584 J is option C: 10.6 J.

Answer 2

Answer:The book's potential energy will be converted entirely to kinetic energy at that point in the fall, since we can neglect losses due to air resistance. The potential energy is given by PE=mgh, where m=1.2kg, h=0.9m, and g=9.81m/s^2. This is the acceleration due to gravity.

This gives:

PE=1.2*0.9*9.81=10.59J

This is also the kinetic (mechanical) energy right before the landing.

Step-by-step explanation: