Page 24 - Fisika Terapan for Engineers and Scientists

224 CHAPTER 7 Work and Energy

✔ Checkup 7.4

y
QUESTION 1: Figure 7.24 shows two roller coasters in profile. Cars are released at the
Concepts
in top of each, from rest. Which, if either, of these roller coasters gives the car a larger
Context
speed at the bottom? Neglect friction.
QUESTION 2: A piano is being moved from the second floor of one house to the second
floor of another, nearby house. Describe the changes in the gravitational potential
energy of the piano during this move.
x
O QUESTION 3: A skidding truck slides down a mountain road, at constant speed. Is the
mechanical energy E K U conserved?
y
QUESTION 4: At an amusement park, a girl jumps off a high tower and lands in a pool.
Meanwhile, a boy slides down a (frictionless) water slide that also takes him from the
tower into the pool.Who reaches the pool with the higher speed? Who reaches the pool
first?
QUESTION 5: A bicyclist rolls down a hill without braking, starting at the top, from rest.
A second bicyclist rolls down the same hill, starting at one-half the height, from rest.
By what factor will the speed of the first bicyclist be larger than that of the second, at
x
O the bottom? Ignore friction.
(A) 22 (B) 2 (C) 222 (D) 4
FIGURE 7.24 Two roller-coaster profiles.
The two plots have the same vertical scale.

SUMMARY

MATH HELP Integrals (page 213)

PROBLEM-SOLVING TECHNIQUES Calculation of Work (page 218)

PROBLEM-SOLVING TECHNIQUES Energy Conservation in Analysis of Motion (page 223)

SI UNIT OF WORK (Unit of energy) joule J N m

WORK DONE BY A CONSTANT FORCE

Parallel to a displacement x W F ¢x F x (7.1)
x
x
#
Not parallel to a displacement s W F s cos u F s (7.6; 7.5)
F
s