2.3 Work, Energy & Power

An object falls from rest from a height h close to the surface of the Moon. The Moon has no atmosphere.

When the object has fallen to height  above the surface, what is

A horizontal spring of spring constant k and negligible mass is compressed through a distance y from its equilibrium length. An object of mass m that moves on a frictionless surface is placed at the end of the spring. The spring is released at speed  v and returns to its equilibrium length.

What is the value of y?

A student states three scenarios in which she thinks no work is done on an object.

1. A pulling force on a sledge being pulled at an angle.
2. A charged particle in a magnetic field.
3. A drag force acting a car.

Which of the above scenarios is / are correct?

The power generated by the nuclear reactions in the core of the reactor is 35 GW.

If the efficiency of the power station is 60%, how much power goes into producing wasted energy?

A mass with speed v travels up to point X then down to Y.

Assuming air resistance is negligible, what is v of the mass at point Y?

A student of mass 50 kg climbs a vertical ladder 4.0 m tall in a time of 8.0 s. What is the power developed by the student against gravity?

The efficiency of an electric motor is 80 %. When lifting a body, the amount of energy wasted is . What is the useful work done by the motor?

A lift is operated by an electric motor. It moves between the 21^st and the 5^th floor at a constant speed. One main energy transformation during this journey is:

A spring of mass m and spring constant k rests on top of a vertical spring whose base is attached to the floor.

What is the energy stored by the spring?