Deck 3: Falling Objects and Projectile Motion

Question 1

The acceleration due to the Earth's gravity, in English units, is 32 ft/s². In the absence of air friction, a ball is dropped from rest. Its speed on striking the ground is exactly 60 miles/hr. For what time interval was the ball falling? (There are 5280 feet in one mile.)

A) 5 s
B) 6.1 s
C) 4.125 s
D) 2.75 s

Answer 1

4.125 s

Question 2

If you drop a ball in the absence of air resistance, it accelerates downward at 9.8 m/s². If instead you throw the ball upward, then its downward acceleration after release is

A) less than 9.8 m/s².
B) equal to 9.8 m/s².
C) greater than 9.8 m/s².

Answer 2

equal to 9.8 m/s².

Question 3

The acceleration due to the Earth's gravity, in English units, is 32 ft/s². In the absence of air friction, a ball is dropped from rest. Its speed on striking the ground is exactly 132 ft/s. From what height was the ball dropped?

A) 165 ft
B) 272 ft
C) 132 ft
D) 421 ft

Answer 3

272 ft

Question 4

Suppose you throw a ball vertically downward with a speed of 10 m/s. Neglecting air friction, what would be the speed of the ball one second later?

A) -9.8 m/s²
B) 9.8 m/s²
C) 15 m/s
D) 19.8 m/s
E) 24.8 m/s

Question 5

A body released from rest falls with an acceleration of 9.8 m/s². If the same body is thrown upward at an angle, and air resistance is negligible, its acceleration after release will be

A) downward and less than 9.8 m/s².
B) downward and equal to 9.8 m/s².
C) downward and greater than 9.8 m/s².
D) upward and equal to 9.8 m/s².
E) upward and greater than 9.8 m/s².

Question 6

An object rises at 5.0 m/s under the influence of gravity only. One second later the object is

A) rising at 4.8 m/s.
B) rising at 5 m/s.
C) neither rising nor falling.
D) falling at 4.8 m/s.

Question 7

A person standing at the edge of a cliff throws one rock straight up and another rock straight down at the same initial speed. The rock that was thrown __________ has less speed at impact.

A) upward
B) downward
C) Actually, each rock has the same speed just before impact.

Question 8

Which of the curves in the figure best shows the speed of an object falling from rest without air friction?

A) A
B) B
C) C

Question 9

A rifle bullet is fired horizontally at the same instant another bullet is allowed to drop from rest at the same height. Which bullet strikes the earth first?

A) The bullet from the rifle
B) The bullet allowed to drop
C) Both strike at the same instant.

Question 10

Neglecting friction, if a Cadillac and Volkswagen start rolling down a hill together, the heavier Cadillac will get to the bottom

A) before the Volkswagen.
B) after the Volkswagen.
C) at the same time as the Volkswagen.

Question 11

A football is thrown upward at some angle above the horizontal. If we neglect air friction, then we can conclude that the acceleration vector of the football is

A) opposite to the velocity vector.
B) zero.
C) along the direction of motion.
D) down.

Question 12

A ball is thrown straight up. It reaches its highest point and then falls back. Which of the following is the correct statement?

A) Throughout its motion, the ball's velocity is zero.
B) At the highest point in its motion, the ball's acceleration is zero.
C) At the highest point in its motion, the ball's velocity is zero.
D) Throughout its motion, the ball's acceleration is zero.
E) At the highest point in its motion, the ball's velocity and acceleration are zero.

Question 13

A stone is thrown upward from a bridge at a speed of 10 m/s. It narrowly misses the bridge on the way back down and hits the water at 30 m/s. The bridge is about

A) 3 m high.
B) 20 m high.
C) 50.5 m high.
D) 76.5 m high.

Question 14

In order to find the depth of a well, you drop a stone into it and time its fall. It hits the water after falling for 1.5 s. The depth of the well is about

A) 7.35 m.
B) 11 m.
C) 14 m.
D) 20 m.

Question 15

A 10 kg object dropped from a certain window strikes the ground in 4.0 s. Neglecting air resistance, a 5 kg object dropped from the same window strikes the ground in

A) 1.0 s.
B) 2.0 s.
C) 4.0 s.
D) 8.0 s.

Question 16

An iron robot falls from rest at a great height. Neglecting air resistance, what is its speed after it has fallen for 3.5 seconds?

A) 9.8 m/s
B) 9.8 m/s²
C) 13.3 m/s
D) 34.3 m/s

Question 17

A bullet is fired straight down from a hovering helicopter. If we neglect air friction, then the velocity of the bullet

A) increases at 9.8 m/s each second.
B) is a constant.
C) is zero.
D) decreases at 9.8 ft/s during the flight.

Question 18

An iron robot falls from rest at a great height. Neglecting air resistance, what distance has it fallen in the first 3.5 seconds?

A) 31 m
B) 60 m
C) 49 m
D) 98 m

Question 19

In a laboratory on Earth, all the air is pumped from a large tube. A feather and a steel ball are simultaneously released from rest inside the tube. What happens next?

A) Both objects float weightless inside the tube.
B) The steel ball falls and hits the bottom before the feather.
C) The feather falls and hits the bottom before the steel ball.
D) Both objects fall and hit the bottom at the same time.

Question 20

You toss a ball straight up in the air. At the highest point, the ball's

A) velocity and acceleration are zero.
B) acceleration is zero but not its velocity.
C) velocity is zero and the acceleration is downward.
D) velocity is zero and the acceleration is upward.

Question 21

A ball is allowed to drop from rest. If the upward direction is positive, then after 2 seconds its velocity will be

A) -19.6 m/s.
B) -9.8 m/s.
C) 9.8 m/s.
D) 19.6 m/s.

Question 22

A man standing on a bridge throws a stone horizontally with a speed of 20 m/s. The stone hits the water below 2.5 s later. The bridge is

A) 44.1 m high.
B) 60.1 m high.
C) 30.6 m high.
D) 20.3 m high.

Question 23

The acceleration of a body is given by the slope of a graph plotting

A) distance travelled versus time.
B) time versus velocity.
C) velocity versus distance travelled.
D) velocity versus time.
E) time versus distance travelled.

Question 24

After 1 second, a ball dropped from rest will have fallen

A) 1.0 m.
B) 2.45 m.
C) 4.9 m.
D) 9.8 m.
E) 19.6 m.

Question 25

One day while measuring acceleration with his pulse as a timing source, Galileo became so excited that his pulse rate increased. His results for acceleration that day were probably

A) higher than usual.
B) lower than usual.
C) more accurate than usual.
D) unchanged.

Question 26

A ball is thrown across the street. During its flight, the ball's speed is lowest at

A) the beginning of its flight.
B) the end of its flight.
C) the highest point of its flight.
D) the speed is constant throughout the flight.

Question 27

A 10 pound iron ball and a 2 pound iron ball are dropped simultaneously from a height of 100 meters. Neglecting air resistance, which ball will reach the ground first?

A) The 10 lb ball
B) The 2 lb ball
C) They will reach the ground at the same time.

Question 28

A ball rolls off a shelf and hits the floor below 0.25 second later. To find the speed of the ball as it left the shelf, we would need

A) the distance measured along the floor to the point of impact.
B) to repeat the experiment.
C) the height of the table.
D) the weight of the ball.

Question 29

During the first 5 seconds after a ball is dropped from rest, how far will it fall?

A) 25 m
B) 61.3 m
C) 122.5 m
D) 245 m
E) 490 m

Question 30

The motion of a falling object is commonly investigated with the aid of a

A) stethoscope.
B) microscope.
C) kaleidoscope.
D) stroboscope.

Question 31

Ball A is thrown upward with a velocity of 19.6 m/s. Two seconds later ball B is thrown upward with a velocity of 9.8 m/s. Which ball is first to return to the thrower's hand?

A) A will arrive first.
B) A and B will arrive at the same time.
C) B will arrive first.

Question 32

A ball thrown upward reaches its maximum height and then falls back. If air resistance is negligible, its acceleration is

A) less on the way up than on the way down.
B) less on the way down than on the way up.
C) the same up and down but zero at the top.
D) the same at all points in the motion.

Question 33

A ball is projected upward with an initial velocity of 10 m/s. It will reach its maximum height in approximately

A) 1 s.
B) 1.5 s.
C) 2 s.
D) 2.5 s.
E) 3 s.

Question 34

Which of the following does not move like a projectile?

A) A monkey jumping from a tree
B) The seeds at a watermelon seed spitting contest
C) An airplane flying at a constant altitude
D) A rock kicked up by a truck wheel

Question 35

The acceleration due to gravity near the surface of Mars is about one-third of the value near the Earth's surface. If a rock fell from rest for the same amount of time on Mars and Earth, the final speed of the rock would be

A) three times faster than on Earth.
B) the square root of three times faster than on Earth.
C) the same speed as on Earth.
D) the square root of three times slower than on Earth.
E) three times slower than on Earth.

Question 36

If air resistance can be ignored, which of the following graphs will be a straight line for a falling object?

A) Distance travelled versus time.
B) Distance travelled versus velocity.
C) Time versus distance travelled.
D) Velocity versus time.
E) Velocity versus distance travelled.

Question 37

A ball is thrown straight up with an initial velocity of 10 m/s. After 3 seconds its velocity will be

A) -19.4 m/s.
B) -29.4 m/s.
C) 0 m/s.
D) 29.4 m/s.
E) 19.4 m/s.

Question 38

The acceleration due to gravity near the surface of the Moon is about one-sixth of the value near the Earth's surface. If a rock were dropped from equal heights on the Moon and Earth, the time it would take the rock from the Moon to hit the ground would be

A) six times longer than on Earth.
B) the square root of six times longer than on Earth.
C) the same time as on Earth.
D) the square root of six times shorter than on Earth.
E) six times shorter than on Earth.

Question 39

A bullet is fired horizontally at a target 20 m away. The velocity of the bullet as it leaves the gun is 200 m/s. How much, approximately, will the bullet drop on its way to the target?

A) 0.05 m
B) 0.1 m
C) 0.2 m
D) 0.3 m
E) 0.4 m

Question 40

Assuming g = 10 m/s² and that air resistance is negligible, in 1/2 second a ball dropped from rest will fall

A) 0.3 m.
B) 0.8 m.
C) 1.0 m.
D) 1.25 m.
E) 2.25 m.

Question 41

To get a clean "swish"-nothing but net-on the basketball floor, you must shoot the ball so that its velocity vector is at least ________ above horizontal when it gets to the hoop.

A) 45 $\degree$
B) 58 $\degree$
C) 32 $\degree$
D) 30 $\degree$

Question 42

For a bullet fired horizontally, its ___________ velocity will retain a constant non-zero value until it is stopped.

Question 43

A ball is thrown at an upward angle. The horizontal speed of the ball is 20 m/s and the ball covers a distance of 10 m. The maximum height of the arc through which the ball travels is

A) 1.2 m.
B) 4.9 m.
C) 10 m.
D) It cannot be determined from this information.

Question 44

A ___________ is a body whose only acceleration is the downward acceleration due to gravity.

Question 45

During batting practice, two baseballs have the same speed when leaving the bat of Babe Ruth. One ball goes over the outfield fence for a home run, and the other can be caught by an infielder. The difference between the two swings is that the home run ball starts out _________ to 45 $\degree$ .

Question 46

The time of flight of a projectile, fired horizontally over level ground, is independent of its horizontal _________________.

Question 47

Which of the three curves show the speed of an object that is beginning to experience significant air resistance?

A) Object U
B) Object G
C) Object K

Question 48

A football is kicked at an angle, giving it a horizontal velocity of 25 m/s. At the highest point in its path, the football will have a velocity of ________ m/s and a horizontal acceleration of ___________ m/s².

Question 49

A body whose velocity increases by a constant amount each second is exhibiting motion for which the ____________________ is constant.

Question 50

For identical cannons and identical projectiles and identical initial speeds, but different pointing angles, the maximum distance for its projectile is attained for the cannon which launches at

A) 32 $\degree$ above horizontal.
B) 45 $\degree$ above horizontal.
C) either 32 $\degree$ or 58 $\degree$ above horizontal.
D) zero degrees-a flat trajectory.

Question 51

Two projectiles are launched 50 $\degree$ above horizontal but with different initial speeds. Which of the following must be true while the projectiles are in the air? (Ignore air resistance.)

A) The projectiles will reach the same maximum height.
B) The horizontal speeds of both projectiles are the same.
C) The horizontal accelerations of both projectiles are the same: zero.
D) The one with larger initial speed will experience a larger vertical acceleration.

Question 52

A baseball pitcher throws a fastball at 98 mph. He also has a slower "changeup" pitch, 75 mph, which he throws identically, same windup and same release angle from shoulder height. Which pitch gets to home plate with a flatter trajectory-i.e., velocity vector closer to horizontal?

A) The fastball
B) The changeup
C) They each have same trajectory, since the distance to home plate is the same.
Fill in the Blank Questions

Question 53

Which of these graphs would be correct for the speed of a ball thrown upward?

A) A
B) B
C) C
D) D

Question 54

Two people stand on different floors of an outdoor stairway. One is 6 m above the ground and the other is 12 m above the ground. The person on the lower floor throws a ball upward with a speed of 15 m/s and the other person just drops hers. Ignoring air resistance, which ball hits the ground at a higher speed?

A) The one thrown upward.
B) The one that is dropped.
C) They both hit the ground with the same speed.