### Concept Items

### 9.1 Work, Power, and the Work–Energy Theorem

- No, because the work-energy theorem states that work done on an object is equal to the change in kinetic energy, and change in KE requires a change in velocity. It is assumed that mass is constant.
- No, because the work-energy theorem states that work done on an object is equal to the sum of kinetic energy, and the change in KE requires a change in displacement. It is assumed that mass is constant.
- Yes, because the work-energy theorem states that work done on an object is equal to the change in kinetic energy, and change in KE requires a change in velocity. It is assumed that mass is constant.
- Yes, because the work-energy theorem states that work done on an object is equal to the sum of kinetic energy, and the change in KE requires a change in displacement. It is assumed that mass is constant.

- Work is defined as the ratio of the force over the distance.
- Work is defined as the sum of the force and the distance.
- Work is defined as the square of the force over the distance.
- Work is defined as the product of the force and the distance.

A book with a mass of 0.30 kg falls 2 m from a shelf to the floor. This event is described by the work–energy theorem: $$W=\text{}fd\text{=}\frac{1}{2}m{v}_{2}^{2}-\frac{1}{2}m{v}_{1}^{2}$$ Explain why this is enough information to calculate the speed with which the book hits the floor.

- The mass of the book,
*m*, and distance,*d*, are stated.*F*is the weight of the book*mg . v*_{1}is the initial velocity and*v*_{2}is the final velocity. The final velocity is the only unknown quantity. - The mass of the book,
*m*, and distance,*d*, are stated.*F*is the weight of the book*mg . v*_{1}is the final velocity and*v*_{2}is the initial velocity. The final velocity is the only unknown quantity. - The mass of the book,
*m*, and distance,*d*, are stated.*F*is the weight of the book*mg . v*_{1}is the initial velocity and*v*_{2}is the final velocity. The final velocity and the initial velocities are the only unknown quantities. - The mass of the book,
*m*, and distance,*d*, are stated.*F*is the weight of the book*mg . v*_{1}is the final velocity and*v*_{2}is the initial velocity. The final velocity and the initial velocities are the only unknown quantities.

### 9.2 Mechanical Energy and Conservation of Energy

- While going up, the person’s KE would change to PE. While coming down, the person’s PE would change to KE.
- While going up, the person’s PE would change to KE. While coming down, the person’s KE would change to PE.
- While going up, the person’s KE would not change, but while coming down, the person’s PE would change to KE.
- While going up, the person’s PE would change to KE, but while coming down, the person’s KE would not change.

- $v=h$
- $v=\sqrt{2h}$
- $v=gh$
- $v=\sqrt{2gh}$

The starting line of a cross country foot race is at the bottom of a hill. Which form(s) of mechanical energy of the runners will change when the starting gun is fired?

- Kinetic energy only
- Potential energy only
- Both kinetic and potential energy
- Neither kinetic nor potential energy

### 9.3 Simple Machines

- It reduces the input force and the output force.
- It reduces the input force and increases the output force.
- It increases the input force and reduces the output force.
- It increases the input force and the output force.

Which type of simple machine is a knife?

- A ramp
- A wedge
- A pulley
- A screw