100% 4 Rated
Attempts 127

An electromagnet is holding a 1,500-kg car at a height of 25 m above the ground. The magnet then experiences a power outage, and the car falls to the ground. Which of the following is false?

  1. A
    The car had a potential energy of 367.5 kJ.
  2. B
    367.5 kJ of potential energy is converted to kinetic energy.
  3. C
    The car retains potential energy of 367.5 kJ when it hits the ground.
  4. D
    The car’s potential energy converts to kinetic energy and then to sound energy.

Topic Flashcards

Click to Flip
Question

Calculate the gravitational potential energy (GPE) of the 1,500-kg car held at 25 m. Using the principle of conservation of energy (ignoring air resistance), determine the car's velocity the moment before it hits the ground.

Answer

GPE = mgh = (1500 kg)(9.8 m/s²)(25 m) = 367,500 J or 367.5 kJ. Before impact, all GPE is converted to Kinetic Energy (KE): KE = ½mv² = 367,500 J. Solving for v: v = √(2KE/m) = √(2*367500/1500) = √(490) ≈ 22.1 m/s.

Question

In a real-world scenario, air resistance is present. How does this affect the energy conversion described in the problem? Specifically, what happens to the final kinetic energy and velocity compared to the ideal calculation?

Answer

Air resistance does work against the car, converting some of the car's mechanical energy (GPE) into thermal energy (heat) and sound in the air. Therefore, the final kinetic energy upon impact is less than 367.5 kJ, and the final velocity is less than the calculated 22.1 m/s. Total energy is still conserved, but it is no longer confined to just GPE and KE.

Question

The false statement is that the car retains GPE at ground level. If we define the ground as our zero reference point (h=0), what is the car's GPE at that moment? If, instead, we defined a reference point 10 meters below the ground, what would the car's GPE be upon impact?

Answer

With ground as h=0: GPE = mg(0) = 0 J. With a point 10m below as h=0: At impact, the car's height is h = +10m relative to that new zero. GPE = (1500)(9.8)(10) = 147 kJ. This teaches that GPE values are relative and depend on the chosen reference level, but changes in GPE are absolute.

Question

Statement D says energy converts to kinetic and then to sound. Detail the primary energy transformations from the moment of the power outage until the car is at rest on the ground.

Answer

GPE → Kinetic Energy → Internal Energy (Thermal/Heat) and Sound Energy. As the car falls, GPE converts to KE. Upon impact, KE is transferred: 1) to the car and ground as deformation (converted to heat), 2) to vibrational energy in the air and materials (sound), and 3) possibly to other forms like light (sparks).

Question

If the car's mass were doubled to 3,000 kg but still dropped from 25 m, how would the following change: a) Initial GPE, b) Final velocity just before impact (ignoring air resistance), c) The falsity of statement C?

Answer

a) Initial GPE doubles to 735 kJ (GPE is directly proportional to mass). b) Final velocity remains unchanged at ~22.1 m/s. In the equation v = √(2gh), mass cancels out. c) Statement C ("retains potential energy...") remains false. Regardless of mass, GPE at zero height is always zero relative to that point.

Mini Quiz

1 / 3
Is the gravitational potential energy of an object solely determined by its mass and its height above a chosen reference point?

Related Questions

Top Picks
Why does potential energy increase as particles approach each other?
A transverse wave does not have ___________.
How do a scalar quantity and a vector quantity differ?
Which one has the highest density?
A 5-cm candle is placed 20 cm away from a concave mirror with a focal length of 15 cm. About what is the image height of the candle in the mirror?
Available Test Sets
HESI A2 Anatomy & Physiology Practice Test
HESI A2 Biology Practice Test
HESI A2 Chemistry Practice Test
HESI A2 Vocabulary Practice Test
HESI A2 Grammar Practice Test
HESI A2 Reading Comprehension Practice Test
HESI A2 Mathematics Practice Test
NEX Math Free Practice
NEX Science Free Practice
NEX Verbal Reasoning Free Practice
ATI RN Mental Health Practice Test
Available FREE Test Sets
HESI Admission Assessment A2 Exam Physics
HESI Physics Practice Test
HESI Physical Assessment