Work, power and energy
Work, collision, power, energy and impulse
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Time limit: 50 minutes
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Question 1
What is the correct definition of work in physics?
Explanation
Work is defined as the transfer of energy through motion, where a force causes an object to move a certain distance.
Question 2
Which term describes the effect that occurs when two objects collide?
Explanation
Impulse is the change in momentum resulting from a collision, measuring the effect of a force over time.
Question 3
Which of the following defines power in physics?
Explanation
Power is defined as the rate at which work is done, indicating how quickly energy is transferred.
Question 4
What does energy refer to in physics?
Explanation
Energy is defined as the capacity to do work, allowing for the performance of tasks or actions.
Question 5
Impulse is measured as the product of which two quantities?
Explanation
Impulse is measured as the product of force and the time duration for which the force acts, indicating the influence of the force over that period.
Question 6
A car of mass 1000 kg is traveling at a speed of 20 m/s when it collides with a stationary wall, bringing the vehicle to a stop in 0.5 seconds. Calculate the impulse experienced by the car during the collision.
Explanation
Impulse can be calculated as the change in momentum. The momentum before the collision is mass times velocity (1000 kg * 20 m/s = 20000 kg·m/s). The final momentum after the collision is 0 kg·m/s, hence, the change in momentum, or impulse, is 20000 kg·m/s - 0 = 20000 Ns. Since impulse equals force multiplied by time and the force can be derived from the impulse value, in this case, the correct option is 10000 Ns (as calculated in the correct manner). The other options either miscalculate based on different interpretations or misunderstand the concept of impulse.
Question 7
An engineer is analyzing two collisions: Collision A involves two objects of identical mass colliding elastically, whereas Collision B involves two objects of different masses colliding inelastically. Which statement best describes the relationship between energy, work, and the type of collisions?
Explanation
Collision A conserves total kinetic energy and does not conduct work on the system, while in Collision B, kinetic energy is not conserved due to energy being transformed into internal energy (heat, sound, or deformation) as the objects collide. Therefore, the correct statement is that work done in Collision B results in deformation. The other options misrepresent the principles of energy conservation and work.
Question 8
[Case Scenario] A car of mass 1200 kg is initially at rest when it collides with a stationary truck of mass 6000 kg. The collision is perfectly inelastic, meaning the two vehicles stick together after the impact. The car strikes the truck with a speed of 15 m/s. After the collision, they move together as a single mass. Based on the principles of momentum and energy, what is the total kinetic energy of the system just after the collision? Question: What is the total kinetic energy of the car and truck combined after the collision?
Explanation
The total kinetic energy after an inelastic collision is lower than the initial kinetic energy of the moving object due to energy loss. The combined speed of the car and truck is calculated using conservation of momentum, which needs to be inserted into the kinetic energy formula for final calculations.
Question 9
[Case Scenario] A 5 kg ball is thrown vertically upwards with an initial speed of 20 m/s. As it rises, the kinetic energy decreases while the gravitational potential energy increases until it reaches a maximum height. Assuming no air resistance, calculate the height reached by the ball at its peak. Question: What maximum height does the ball reach based on the conversion of kinetic energy to gravitational potential energy?
Explanation
The kinetic energy at the moment of release is converted into gravitational potential energy at the peak height. By setting the kinetic energy equal to gravitational potential energy, the height can be found. The formulas for kinetic energy (KE = 0.5 * m * v^2) and potential energy (PE = m * g * h) are applied for this calculation.
Question 10
[Case Scenario] A cyclist is pedaling with a constant power output of 200 W. If the cyclist uses this power to maintain a speed of 5 m/s over flat ground, calculate the force exerted by the cyclist against friction and air resistance. Note that power is calculated as the product of force and velocity (P = F * v). Question: What is the force exerted by the cyclist in this scenario?
Explanation
The calculation of the force is derived directly from the relationship between power and velocity. By substituting the known values into the power formula, we can find that the correct force exerted is 40 N, which aligns with the mechanics presented in work and energy definitions.