Unit 3 Section 1 Practice Scrimmage

What is the formula for calculating work done by a constant force?

Answer explanation

The formula for calculating work done by a constant force is W=F⋅d, where W is work, F is the force applied, and d is the distance moved in the direction of the force. This choice correctly represents the relationship between these variables.

A force of 10 N is applied to move an object 5 meters in the direction of the force. Calculate the work done.

• 15 J

• 50 J

• 5 J

• 25 J

Answer explanation

Work done is calculated using the formula: Work = Force × Distance. Here, Work = 10 N × 5 m = 50 J. Therefore, the correct answer is 50 J.

Which of the following best describes kinetic energy?

• Energy stored in an object due to its position

• Energy an object possesses due to its motion

• Energy stored in chemical bonds

• Energy due to temperature

Answer explanation

Kinetic energy is defined as the energy an object possesses due to its motion. This distinguishes it from potential energy, which is related to an object's position, and other forms of energy like chemical or thermal energy.

Calculate the kinetic energy of a 2 kg object moving at a velocity of 3 m/s.

• 9 J

• 18 J

• 6 J

• 12 J

Answer explanation

The kinetic energy (KE) is calculated using the formula KE = 0.5 * m * v^2. For a 2 kg object at 3 m/s: KE = 0.5 * 2 * (3^2) = 0.5 * 2 * 9 = 9 J. Thus, the correct answer is 9 J.

• 490 J

• 50 J

• 98 J

• 500 J

Answer explanation

The potential energy (PE) is calculated using the formula PE = mgh. Here, m = 5 kg, g = 9.8 m/s², and h = 10 m. Thus, PE = 5 * 9.8 * 10 = 490 J. Therefore, the correct answer is 490 J.

Which of the following statements is true about potential energy?

• It depends on the speed of the object.

• It is always equal to kinetic energy.

• It depends on the position of the object.

• It is not affected by gravity.

Answer explanation

Potential energy depends on the position of an object relative to a reference point, such as height in a gravitational field. The other statements are incorrect as they misrepresent the nature of potential energy.

Explain how energy is conserved in a closed system.

• Energy is created and destroyed.

• Energy is transferred between objects but the total energy remains constant.

• Energy is lost as heat.

• Energy is only present in kinetic form.

Answer explanation

In a closed system, energy is conserved as it can be transferred between objects, but the total amount of energy remains constant. This means energy is neither created nor destroyed, aligning with the law of conservation of energy.

A roller coaster car is at the top of a hill with a potential energy of 1000 J. If it descends and has a kinetic energy of 800 J at the bottom, what is the total mechanical energy of the system?

• 800 J

• 1000 J

• 1800 J

• 200 J

Answer explanation

The total mechanical energy is conserved in the absence of non-conservative forces. At the top, the potential energy is 1000 J. As it descends, the total energy remains 1000 J, regardless of the kinetic energy at the bottom.

Which principle states that the total energy in a closed system remains constant?

• Newton's First Law

• Law of Conservation of Energy

• Law of Thermodynamics

• Law of Inertia

Answer explanation

The Law of Conservation of Energy states that in a closed system, energy cannot be created or destroyed, only transformed. This principle ensures that the total energy remains constant over time.

• 19.8 m/s

• 14 m/s

• 10 m/s

• 20 m/s

Answer explanation

Using the formula for free fall, v = sqrt(2gh), where g = 9.8 m/s² and h = 20 m, we find v = sqrt(2 * 9.8 * 20) = sqrt(392) ≈ 19.8 m/s. Thus, the correct answer is 19.8 m/s.