Paul Peter Urone; Roger Hinrichs

Problems

9.1 Work, Power, and the Work–Energy Theorem

14 .

A baseball player exerts a force of

100\,\text{N}

on a ball for a distance of

0.5\,\text{m}

as he throws it. If the ball has a mass of

0.15\,\text{kg}

, what is its velocity as it leaves his hand?

$-36.5\,\text{m/s}$
$-25.8\,\text{m/s}$
$25.8\,\text{m/s}$
$36.5\,\text{m/s}$

15.

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

16 .

What is the kinetic energy of a

0.01\,\text{kg}

bullet traveling at a velocity of

700\,\text{m/s}

?

$3.5\,\text{J}$
$7\,\text{J}$
$2.45 \times 10^3\,\text{J}$
$2.45 \times 10^5\,\text{J}$

17 .

A marble is rolling across a flat surface with a velocity of 2 m/s. It begins to roll up a ramp. Ignoring rotational kinetic energy and friction, what will be the vertical height of the marble when it comes to a stop before rolling back down?

$0.1\,\text{m}$
$0.2\,\text{m}$
$0.4\,\text{m}$
$2\,\text{m}$

18.

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

19.

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

20.

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?

The image is a picture of wire cutters with red handles. The pinchers are closed.

1.34
1.53
33.3
33.5