I post this early ; but didn't understand the answer..
a 3-kg object falls from a height of 10m to the ground. The work done by air resistance ia 20 J. What is the kinetic energy of the object as it hits the ground..
To find the kinetic energy of the object as it hits the ground, we need to first calculate its gravitational potential energy at the initial height and then subtract the work done by air resistance.
1. Calculate the gravitational potential energy (GPE):
The gravitational potential energy is given by the formula: GPE = mgh, where m is the mass, g is the acceleration due to gravity (approximately 9.8 m/s²), and h is the height.
Given:
Mass (m) = 3 kg
Height (h) = 10 m
Acceleration due to gravity (g) = 9.8 m/s²
GPE = 3 kg * 9.8 m/s² * 10 m
GPE = 294 J
2. Subtract the work done by air resistance:
The work done by air resistance is given as -20 J. Since it is subtracted, we change the sign.
Kinetic Energy (KE) = GPE - Work done by air resistance
KE = 294 J - (-20 J)
KE = 294 J + 20 J
KE = 314 J
Therefore, the kinetic energy of the object as it hits the ground is 314 Joules.