91影视

Alan leaves Los Angeles at 8:00 a.m. to drive to San Francisco, 400 mi away. He travels at a steady 50 mph. Beth leaves Los Angeles at 9:00 a.m. and drives a steady 60 mph. a. Who gets to San Francisco first? b. How long does the first to arrive have to wait for the second?

For Questions 1 through 3, interpret the position graph given in each

figure by writing a very short 鈥渟tory鈥� of what is happening. Be creative!

Have characters and situations! Simply saying that 鈥渁 car moves

100 meters to the right鈥� doesn鈥檛 qualify as a story. Your stories should

make specific reference to information you obtain from the graph, such

as distance moved or time elapsed.

A bicycle is traveling east. Can its acceleration vector ever point west? Explain.

FIGURE EX2.7 showed the velocity graph of blood in the aorta. What is the blood鈥檚 acceleration during each phase of the motion, speeding up and slowing down?

FIGURE EX2.11 shows the velocity graph of a particle moving along the x-axis. Its initial position is x0 = 2.0 m at t0 = 0 s. At t = 2.0 s, what are the particle鈥檚 (a) position, (b) velocity, and (c) acceleration?

(a) Give an example of a vertical motion with a positive velocity and a negative acceleration. (b) Give an example of a vertical motion with a negative velocity and a negative acceleration.

A ball is thrown straight up into the air. At each of the following

instants, is the magnitude of the ball鈥檚 acceleration greater than g,

equal to g, less than g, or 0? Explain.

a. Just after leaving your hand.

b. At the very top (maximum height).

c. Just before hitting the ground.

FIGURE EX2.12 shows the velocity-versus-time graph for a particle moving along the x-axis. Its initial position is x0 = 2.0 m at t0 = 0 s. a. What are the particle鈥檚 position, velocity, and acceleration at t = 1.0 s? b. What are the particle鈥檚 position, velocity, and acceleration at t = 3.0 s?

a. What constant acceleration, in SI units, must a car have to go from zero to 60 mph in 10 s? b. How far has the car traveled when it reaches 60 mph? Give your answer both in SI units and in feet.

A rock is thrown (not dropped) straight down from a bridge into the

river below. At each of the following instants, is the magnitude of the rock鈥檚 acceleration greater than g, equal to g, less than g, or 0? Explain.

a. Immediately after being released.

b. Just before hitting the water.