Problems
9.1 Work, Power, and the Workâ€“Energy Theorem

36.5\,\text{m/s}

25.8\,\text{m/s}

25.8\,\text{m/s}

36.5\,\text{m/s}
A boy pushes his little sister on a sled. The sled accelerates from 0 to 3.2 m/s . If the combined mass of his sister and the sled is 40.0 kg and 18 W of power were generated, how long did the boy push the sled?
 205 s
 128 s
 23 s
 11 s
9.2 Mechanical Energy and Conservation of Energy

3.5\,\text{J}

7\,\text{J}

2.45 \times 10^3\,\text{J}

2.45 \times 10^5\,\text{J}

0.1\,\text{m}

0.2\,\text{m}

0.4\,\text{m}

2\,\text{m}
The potential energy stored in a compressed spring is $$U=\frac{1}{2}k{x}^{2}$$, where k is the force constant and x is the distance the spring is compressed from the equilibrium position. Four experimental setups described below can be used to determine the force constant of a spring. Which one(s) require measurement of the fewest number of variables to determine k? Assume the acceleration due to gravity is known.
 An object is propelled vertically by a compressed spring.
 An object is propelled horizontally on a frictionless surface by a compressed spring.
 An object is statically suspended from a spring.
 An object suspended from a spring is set into oscillatory motion.
 I only
 III only
 I and II only
 III and IV only
9.3 Simple Machines
A man is using a wedge to split a block of wood by hitting the wedge with a hammer. This drives the wedge into the wood creating a crack in the wood. When he hits the wedge with a force of 400 N it travels 4 cm into the wood. This caused the wedge to exert a force of 1,400 N sideways increasing the width of the crack by 1 cm . What is the efficiency of the wedge?
 0.875 percent
 0.14
 0.751
 87.5 percent
An electrician grips the handles of a wire cutter, like the one shown, 10 cm from the pivot and places a wire between the jaws 2 cm from the pivot. If the cutter blades are 2 cm wide and 0.3 cm thick, what is the overall IMA of this complex machine?
 1.34
 1.53
 33.3
 33.5