Classical Mechanics

Kinetic Energy

Understanding Kinetic Energy


Two boats are having a race on a frictionless horizontal lake between two buoys separated by the distance d.d. Boat A has a mass of mm, while boat B has a mass of 2m2m. The boats have identical sails, so the wind exerts the same constant force FF on each of them.

Which boat has the greater kinetic energy as it crosses the finish line?

A car traveling at 50 km/h50\text{ km/h} will move 4444 extra meters from the moment its brakes are applied fully. If the same car travels at 100 km/h100\text{ km/h} on the same road, how far will it move from the instant its brakes are fully applied?

An object with mass 12 kg12\text{ kg} is at rest on a frictionless horizontal floor. If a horizontal force F=40 NF=40\text{ N} is applied on the object until it has moved 10 m,10\text{ m}, what is the object's resulting kinetic energy?

If an object initially at rest starts to fall freely, what happens to its kinetic energy?

Assume that air resistance is negligible.

Which of the following statements is/are true concerning kinetic energy?

I. Kinetic energy is a scalar quantity.

II. The kinetic energy of an object that accelerates uniformly increases linearly.

III. If a moving object changes only its direction and not speed, its kinetic energy does not change.


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