Understanding Work and Energy: Definition, Examples, and Equations

2. 6.1 Work Work is done when a force is applied to an object and the object moves in the direction of the applied force.

3. Example: Work is measured with a unit called the joule. p. 191 3.) 25 J Work is zero if the distance moved is zero. W = Fd W = F x 0 = 0 The boy is holding the weights, which don't move. No work is being done, so why does he get tired? The individual cells in his muscles are contracting and relaxing as he holds the weights. The muscles cells are doing work, but no work is done on the weights because they are at rest the whole time.

4. The angle of the force affects the work done. p. 193 5.) 0.17 kJ

5. Work can be positive, negative, or zero. W = -Fd (when 0 = 180o) W = 0 (when 0 = 90o) p. 194 B<A<C<D

6. The work done by separate forces can be summed. Wtotal = W1 + W2 + W3+... p.196 8.) W = Fd 9.) Use the component of the force in the direction of the displacement. 10.) No, the displacement will be zero. 11. a) not possible b.) work done when sliding book is brought to rest by friction

7. 6.2 Work and Energy Kinetic Energy The energy of motion depends on mass and speed. Doing work on an object changes its speed.

8. p. 199 16.) 0.47 J 17.) 1200 kg 18.) 32 m/s Work and kinetic energy are related. p.201 20. a) 7.2 J b) 11 m/s c) 18 J p. 201

9. Potential Energy: stored energy. Two types: Gravitational Elastic Potential energy, like all energy, is measured in joules (J), the same unit used for work. p. 206 27.) doubles, triples 28.) increase, positive work increases kinetic energy 29.) negative, the work is negative because the change in KE is negative 30.) no, because the weight of the box is different in each case. 31.) increases by a factor of 4