Homework solution
Chapter 10
Dr. Ray Kwok
SJSU
Kinematics - Dr. Ray Kwok
Chapter 10
1. In synchronized diving, divers remain in the air for the same time. Is
this possible if they have different weights? Defend your answer.
Falling speed is independent of weight, providing they have similar
built (almost the same air resistance – small effect)
3. Suppose you roll a ball off a tabletop. Compared with a slow roll, will a
faster-moving ball hit the floor with a higher speed? Defend your
answer.
Yes. While the vertical speed would be the same, a faster moving ball
means it has a higher horizontal speed throughout the path. Therefore
the resultant speed would be higher.
Kinematics - Dr. Ray Kwok
6. Suppose you drop an object from an airplane traveling at constant
velocity, and further suppose that air resistance doesn’t affect the
falling object, What will be its falling path as observed by someone at
rest on the ground, not directly below but off to the side where a clear
view can be seen? What will be the falling path as observed by you
looking downward from the airplane? Where will the object strike the
ground, relative to you in the airplane? Where will it strike in the more
realistic case in which air resistance does affect the fall?
The path of the object would be parabolic as observed by someone on
the ground.
As viewed by someone on the plane, the object would fall straight
down because you and the object have the same horizontal speed.
The object will strike the ground directly beneath you. Of course the
ground is constantly moving backward according to you.
Air resistance will slow down the package so it will go slower than you
do horizontally. Therefore, it will strike the ground behind you.
Kinematics - Dr. Ray Kwok
9. At what point in its trajectory does a batted baseball have its minimum
speed? If air drag can be neglected, how does this compare with the
horizontal component of its velocity at other points?
When it’s at its peak. At that position, the baseball has only a
horizontal speed and no vertical component.
This horizontal speed is constant throughout the whole path.
12. Two golfers each hit a ball at the same speed, but one at 60 degrees
with the horizontal and the other at 30 degrees. Which ball goes
farther? Which hits the ground first? (Ignore air resistance)
They reach the ground at the same point. (Complementary angles)
They both have the same initial speed, but the 60 degrees ball has to
travel a longer path, so it will take longer. i.e. the 30 degrees ball will
hit the ground first.