4.4.3 Solving Problems Using Conservation of Mechanical Energy Flashcards
Solving Problems Using Conservation of Mechanical Energy
- You can use conservation of mechanical energy when all the forces acting on a system are conservative forces.
- Conservation of mechanical energy allows you to solve many types of physics problems that would be difficult to solveusing Newton’s laws
Consider an elevator with a mass of 1200 kg, falling from a height of 50 m. A spring is at the bottom and has a spring constant of 5600 N / m. If the elevator activates a set of brakes as soon as it begins to fall, and these brakes apply a constant frictional force of 10,000 N, how much would the spring be compressed?
5.6 m
Assume that a huge spring is at the bottom of an elevator shaft and has a spring constant of 5,600 N / m. The elevator has a mass of 1200 kg, and is falling from a height of 50 m. Which of the following is how much the falling elevator will compress the spring?
14.5 m
If mechanical energy is conserved, why does a ball rolling on a flat horizontal surface eventually stop?
Air friction works against the ball’s motion.
The cable of an elevator with a mass of 1,200 kg snaps, causing it to fall 50 m to the ground floor. Which of the following is how fast it is moving when it reaches the ground floor?
31.3 m / s
If a car, moving at 15 m / s, drives over a 30 m cliff, how fast is it moving vertically when it hits the ground?
24.2 m / s
Why would you use conservation of mechanical energy instead of Newton’s second law?
To avoid having to use force diagrams
If two stars collide in space and form a larger spinning star, how is energy being conserved?
Energy goes into rotational kinetic energy.
If a roller coaster starts at a height of 25 m, moving at 20 m / s, how fast will it be moving when it reaches 50 m?
It does not have enough energy to reach 50 m.
