Review Questions Chapter 3 Pages 40-41 #1-18

1. How does a vector quantity differ from a scalar quantity? (3.1) A vector quantity includes an objects direction of motion or force. A vector quantity has both magnitude and direction. A scalar quantity only includes magnitude.

2. Why is speed classified as a scalar quantity and velocity classified as a vector quantity? (3.1) Speed has no particular direction, velocity specifies direction. Speed = scalar Velocity = vector

What velocity would 0.5 cm equal? 1.5 cm? ANSWER: 5 km/h and 15 km/h 3. If a vector that is 1 cm long represents a velocity of 10 km/h, what velocity does a vector 2 cm long drawn to the same scale represent?(3.2) If 1 cm = 10 km/h Then 2 cm = 20 km/h 3 cm = 30 km/h What velocity would 0.5 cm equal? 1.5 cm? ANSWER: 5 km/h and 15 km/h

The diagonal represents the resultant velocities. 4. When a rectangle is constructed in order to add velocities, what represents the resultant of velocities? (3.2) The diagonal represents the resultant velocities.

5. Why do we say a rectangle is a special case of a parallelogram. (3 A rectangle is a special case of parallelogram because if has four sides, with two pairs of sides parallel to each other. Also a rectangle has right angles.

The vector will be larger. 6. Will a vector at 45o to the horizontal be larger or smaller than its horizontal and vertical components? By how much? (3.3) The vector will be larger. The vector will be the square root of 2 or 1.414 times greater than either of its components.

7. Why does a bowling ball move without acceleration when it rolls along a bowling alley? (3.4) There is no acceleration because there is no horizontal component of force. The only force acting on the bowling ball once it is released from the bowler’s hand, is the vertical force of gravitational acceleration.

8. In the absence of air resistance, why does the horizontal component of velocity for a projectile remain constant while the vertical component changes? (3.4) The only force acting on a projectile is gravitational acceleration. “g” does not have a horizontal component, therefore there is no change to the horizontal velocity.

Both are under the influence of gravity. 9. How does the downward component of the motion of a projectile compare with the motion of free fall? (3.4) The downward component of a projectile’s motion and the motion of free fall are the same. Both are under the influence of gravity.

10. At the instant a ball is thrown horizontally over a level range, a ball held at the side of the first is released and drops to the ground. If air resistance is neglected, which ball strikes the ground first? (3.4) They hit the ground at the same time. The only force acting on each ball is the vertical gravitational component.

In one second a projectile will fall 5m. 11a. How far below an initial straight-line path will a projectile fall in one second? (3.5) b. Does your answer depend on the angle of launch or the initial speed of the projectile? (3.5) In one second a projectile will fall 5m. Neither, because the only force acting on a projectile is the gravity. Gravitational force only exerts in the vertical downward direction. Therefore, the vertical displacement (distance) is found using the formula for free fall. d=1/2 gt2

For maximum altitude a slingshot should be orientated straight up. 12. At what angle should a slingshot be oriented for maximum altitude? For maximum horizontal range? (3.5) For maximum altitude a slingshot should be orientated straight up. For maximum horizontal range, a slingshot should be oriented at a 45 degree angle.

It will be moving at 20 m/s when you catch it. 13. Neglecting air resistance, if you throw a ball straight up with a speed of 20 m/s, how fast will it be moving when you catch it? (3.5) It will be moving at 20 m/s when you catch it.

The catching speed will be equal to the throwing speed, 20 m/s. 14. Neglecting air resistance, if you throw a baseball at 20 m/s to your friend at first base, will the catching speed be greater than, equal to, or less than 20 m/s? Does the speed change if air resistance is a factor? (3.5) The catching speed will be equal to the throwing speed, 20 m/s. If air resistance is a factor, the speed will change. Air resistance will slow down the catching speed of the ball.

We call this type of projectile an Earth satellite. 15. What do we call a projectile that continually “falls” around the Earth? (3.6) We call this type of projectile an Earth satellite.

16. How fast must a projectile moving horizontally travel so that the curve it follows matches the curve of the Earth? (3.6) It must travel approximately 8 km/s (18 000 mi/h) if the satellite is close to the Earth.

17. Why is it important that such a satellite be above Earth’s atmosphere? (3.6) It is important so the satellite avoids the heating effects of atmospheric friction.

18. What force acts on a satellite that is above the Earth’s atmosphere? (3.6) The only force that acts on a satellite that is above the Earth’s atmosphere is gravity. This is truly a “friction free physics world” because there is no air resistance beyond the Earth’s atmosphere.