Text questions that are similar to the ones below:
CQ 2.7, 2.13, 2.15, 2.20, 2.21
P 2.8, 2.9, 2.21, 2.26, 2.28, 2.29, 2.38, 2.41, 2.46, 2.47
Conceptual Questions:
1. Describe what is meant by instantaneous velocity. Give several examples from everyday life. (CQ-2.7)
2. Consider one-dimensional motion, with acceleration. Define the direction of positive displacement. Describe what positive and negative velocity and acceleration mean. Can the velocity be positive and the acceleration negative at the same time? If so, what is happening to the object? (CQ-2.13)
3. Be prepared to answer the quantitiative parts of text conceptual questions 2.20 and 2.21. These questions show graphs of displacement vs. time, and ask where the velocity is highest, lowest, and what the directions of acceleration are.
4. A baseball catcher throws a ball vertically upward and catches it in the same spot when it returns to his mitt. At what point in the ball's path does it experience zero velocity and non-zero acceleration at the same time? (CQ-2.15)
a. Midway on the way up.
b. At the top of its trajectory.
c. The instant it leaves the catcher's hand.
d. The instant before it arrives in the catcher's mitt.
Numerical Problems:
1. A ball is pushed with an initial velocity of 4.0 m/s. The ball rolls down a hill with a constant acceleration of 1.6 m/s2. The ball reaches the bottom of the hill in 8.0 s. What is the ball's velocity at the bottom of the hill? (P-2.21)
2. A rock is thrown straight down from a cliff with an initial velocity of 14.5 m/s. What is the rock's displacement after 2.0 s (acceleration due to gravity is 9.8 m/s2)? (P-2.38)
ans: 49 m.
3. A rock is thrown straight up with an initial velocity of 24.5 m/s. What maximum height will the rock reach before starting to fall downward (acceleration due to gravity is 9.8 m/s2)? (P-2.41)
4. A rock is thrown straight up with an initial velocity of 19.6 m/s. What time interval elapses between the rock's being thrown and its return to the original launch point? (P-2.41)
ans: 4.0 s.
5. A bird, accelerating from rest at a constant rate, experiences a displacement of 28 m in 11 s. What is the final velocity after 10 s? (P-2.28)
6. A bird, accelerating from rest at a constant rate, experiences a displacement of 28 m in 11 s. What is its acceleration? (P-2.29)
ans: 0.46 m/s2.
7. A baseball is released at rest from the top of the Washington Monument. It hits the ground after falling for 6.0 s. What was the height from which the ball was dropped (g = 9.8 m/s2 and assume air resistance is negligible)? (P-2.46)
8. A cheetah can run at approximately 100 km / hr and a gazelle at 80 km / hr. If both animals are running at full speed, with the gazelle starting 70 m ahead, how long before the cheetah catches it? (P-2.8)
ans: 12.6 s.
9. A cheetah can maintain its maximum speed of 100 km / hr for 30 seconds. What minimum distance must a gazelle running 80 km / hr start ahead of the cheetah to escape? (P-2.9)
10. Human reaction time is usually about 0.2 s. If your lab partner holds a ruler between your finger and thumb and releases it without warning, how far can you expect the ruler to fall before you catch it? At least: (P-2.46)
ans: 19.6 cm.
11. An automobile driver puts on the brakes and decelerates from 28 m/s to zero in 12 s. What distance does the car travel? (P-2.26)
12. A 50-gram ball traveling at 25 m/s is bounced off a brick wall and rebounds at 22 m/s. A high-speed camera records this event. If the ball is in contact with the wall for 3.5 ms, what is the average acceleration of the ball during this time interval? (P-2.47)
ans: 13,000 m/s2.