Question

1. a graph of an objects position versus time graph is shown below. which of the following statements about the object is true?

a. the object is in equilibrium.
b. the object is speeding up.
c. the object is slowing down.
d. the object experiences a positive acceleration

1. an ice skater moves across a frozen lake with a constant speed in a straight line. which of the following statements about the skater must be false?

a. the ice skater has an acceleration equal to zero
b. the ice skater is in equilibrium
c. the net force on the skater must not be equal to zero
d. the ice skater has a constant velocity
use the image below for problems 19 and 20
projectile motion
the trajectory of a kicked football

1. in the image above, what is true about the y - component of the velocity at the start and end of its trajectory?

a. the y - component of the velocities are the same
b. the y - component of the velocities are equal in magnitude but opposite in direction
c. the y - component of the velocity at the beginning is greater than the y - component of the velocity at the end.
d. the y - component of the velocities could be the same or different, there is not enough information to tell.

1. in the image above, what is true about the x - component of the velocity at the start and end of its trajectory?

a. the x - component of the velocities are the same
b. the x - component of the velocities are equal in magnitude but opposite in direction
c. the x - component of the velocity at the beginning is greater than the x - component of the velocity at the end.
d. the x - component of the velocities could be the same or different, there is not enough information to tell.

Explanation:

Step1: Analyze position - time graph for question 17

The slope of a position - time graph is velocity. The slope is decreasing, so velocity is decreasing. An object with decreasing velocity is slowing down.

Step2: Analyze ice - skater motion for question 18

An object moving with constant speed in a straight line has zero acceleration ($a = 0$), is in equilibrium (net force $F_{net}=ma = 0$) and has constant velocity. So the false statement is that the net force on the skater must not be equal to zero.

Step3: Analyze projectile motion for question 19

For a projectile, at the same height (start and end of trajectory), the vertical component of velocity has the same magnitude but opposite direction due to the symmetry of the parabola and the action of gravity.

Step4: Analyze projectile motion for question 20

In projectile motion, there is no acceleration in the horizontal ($x$) direction (neglecting air - resistance), so the horizontal component of velocity remains constant throughout the motion.

Answer:

1. c. The object is slowing down.
2. c. The net force on the skater must not be equal to zero
3. b. The y component of the velocities are equal in magnitude but opposite in direction
4. a. The x component of the velocities are the same