work and energy

When is work done on a system?

• when an object moves a distance

• when a force is applied

• when a force is applied through a displacement

• when an object is at rest

Why would a star do no work on a planet that travels in uniform circular motion around it?

• There is no force component parallel to the motion.

• There is no displacement of the planet.

• The planet does not accelerate.

• The star does not exert a force on the planet.

what is your favorite subject ?

• math

• physics

• English

• biology

What is the ability of an object to produce a change in itself or the world around it?

• power

• force

• work

• energy

Which is the rate at which energy is transformed?

• energy

• work

• force

• power

A child holding onto a string attached to a toy boat exerts a force of 8.0 N to pull the boat a distance of 7.2 m along a straight shoreline. If the child holds the string at a 15.0° angle with the horizontal, how much work does she do on the toy boat?

• 14 J

  
  

• 56 J

• 58 J

• 71 J

The weight of a bicyclist and a bicycle together is 53.0 kg. The bicyclist is riding along a straight, level path. How much work is done on the system if the bicyclist slows the bicycle from a speed of 3.84 m/s to 1.27 m/s?

• A. 68.1 J

• 136 J

• 348 J

• 696 J

A boy lifts a stack of six identical books from the floor to a 1.2-m high shelf in 2.5 s. If lifting the books requires 50.8 W of power, what is the mass of each book?

• 1.8 kg

• 0.88 kg

• 1.1 kg

• 2.9 kg

How much work does the force of gravity do on a 5.45-kg bowling ball that falls a distance of 0.755 m?

• 71.2 J

• 40.3 J

• 262 J

• 4.11 J

A student lifts a box of books that weighs 215 N. The box is lifted 1.75 m. What is the change in energy of the box?

• A. 38.4 J

• 376 J

• 225 J

• 123 J