PROJECTILE MOTION HW1 - HON

101. Right left: Use the scale 1 cm: 5 m and draw the positions of the dropped ball at 1-second intervals. Neglect air drag and assume g= 10 m/s2. Estimate the number of seconds the ball is in the air.____________ seconds.

102. Right right: The four positions of the thrown ball with no gravity are at 1-second intervals. At 1 cm: 5 m, carefully draw the positions of the ball with gravity. Neglect air drag and assume g = 10 m/s2. Connect your positions with a smooth curve to show the path of the ball. How is the motion in the vertical direction affected by motion in the horizontal direction?

103. Draw bold vectors to represent the velocity of the ball in the positions shown below. With lighter vectors, show the horizontal and vertical components of velocity for each position. With different color draw acceleration vector in each position.

(a) Which velocity component in the previous question remains constant ? Why?

(b) Which velocity component changes along the path? Why?

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104. A ball tossed upward has initial velocity components 30 m/s vertical, and 5 m/s horizontal. The position of the ball is shown at 1-second intervals. Air resistance is negligible, and g= 10 mIs2. Fill in the boxes, writing in the values of velocity components ascending, and your calculated resultant velocities descending.

1. Which of the following exhibits parabolic motion?a. a person diving into a pool from a diving boardb. a space shuttle orbiting Earthc. a leaf falling from a treed. a train moving along a flat track

2. A bomber flying in level flight must release its bomb before it is over the target. Neglecting air resistance, which one of the following is NOT true?a. The bomber will be over the target when the bomb strikesb. The acceleration of the bomb is constantc. The horizontal velocity of the plane equals the vertical velocity of the bomb when it hits the targetd. The bomb travels in a curved pathe. The time of flight of the bomb is independent of the horizontal speed of the plane

3. A piece of chalk is dropped by a teacher walking at a speed of 1.5 m/s. From the teacher’s perspective, the chalk appears to falla. straight down. c. straight down and forward. d. straight backward.b. straight down and backward.

4. At the instant a ball is thrown horizontally with a large force, an identical ball is dropped from the same height Which ball hits the ground first?a. The horizontally thrown ballb. The dropped ballc. Neither -- they both hit the ground at the same time.

5. At what part of a path does a projectile have minimum speed? a. When it is thrown b. Halfway to the top c. At the top of its path

d. When it returns to the ground e. There's not enough information to say.

6. A dart is thrown horizontally toward X at 20 m/s as shown. It hits Y 0.1 s later. The distance XY is:

7. A boy on the edge of a vertical cliff 20 m high throws a stone horizontally outwards with a speed of 20 m/s. It strikes the ground at what horizontal distance from the foot of the cliff? Use g = 10 m/s2

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8. A track star in the long jump goes into the jump at 12 m/s and launches herself at 20.0° above the horizontal. How long is she in the air before returning to Earth? (g = 9.81 m/s2)

9. A model rocket flies horizontally off the edge of the cliff at a velocity of 50.0 m/s. If the canyon below is 100.0 m deep, how far from the edge of the cliff does the model rocket land?

10. A firefighter 50.0 m away from a burning building directs a stream of water from a fire hose at an angle of 30.00 above the horizontal. If the velocity of the stream is 40.0 m/s, at what height will the stream of water strike the building?

11. Briefly explain why a basketball being thrown toward the hoop is considered projectile motion.

12. An object is uniformly accelerating over time interval of 12 s. Initial velocity is 10 m/s, 00 and after 12 s velocity is 20 m/s, 2700. What is the average velocity during 12 s. What average acceleration is causing this change, both in speed and velocity? Don’t forget to draw a sketch!!!!

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13. Suppose that you are an accident investigator and you are asked whether or not the car was speeding before it crashed through the rail of the bridge and into the mud bank as shown. The speed limit on the bridge is 55 mi/h = 24 m/s. What is your conclusion?

ANSWERS:101. & 102.

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Vertical motion is affected only by gravity: horizontal motion does not affect vertical motion.

103. 104.

1.A 2.C 3.C 4.C 5.C 6. 0.05 m 7. 40 m 8. 0.83 s 9. 225 m 10. 18.7 m 11. Objects sent into the air and subject to gravity exhibit projectile motion. 12. missing13. The car was traveling after it crashed through the rail (it covered 24 m in a time of 1 s, the time to fall vertically 4.9 m). Therefore it must have been traveling faster than 24 m/s before hitting the rail, for some speed was lost in crashing through the rail. Therefore the driver was speeding.

(a) The horizontal component of velocity remains constant because no horizontal force acted.

(b) The vertical component of velocity changes because of acceleration due to gravity.

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