2.4.2 Understanding Projectile Motion

Question 1

Understanding Projectile Motion

Answer 1

• Projectile motion in the x-direction is independent of projectile motion in the y-direction.
• The time required for a projectile to land at the same height at which it began is .
• The range of an object projected from the ground is . The maximal range occurs when the object is projected at an angle of 45°.

Question 2

Suppose that an object is launched at an angle of 30° at a velocity of 45 m / s. How long will it take for the object to hit the ground?

Answer 2

4.6 s

Question 3

Which of the following statements about the velocity as a function of time of a projectile is not correct? Assume that the projectile starts with an initial velocity in the horizontal direction.

Answer 3

After 2 seconds, the object will have a vertical velocity of 19.6 m / s. After 3 seconds, the object will have a vertical velocity of 39.2 m / s.

Question 4

Which of the following statements best describes speed as a function of time of a projectile launched in the horizontal direction?

Answer 4

The speed of the object increases with time.

Question 5

The diagram shows a projectile that is launched in the x-direction at a speed of vi x. Which of the following statements about the horizontal component of the velocity vector is correct?

Answer 5

The horizontal component remains constant with time.

Question 6

Which of the following is not an assumption made about the projectile motion of an object that starts with a given horizontal velocity, vi x?

Answer 6

The acceleration of the object in the y-direction increases with time.

Question 7

Consider an object in projectile motion. You know xi, yi, yf  and vi x. Which of the following general statements best describes how you might find the range of the object?

Answer 7

Use both the equations of kinematics with constant acceleration in the x- and y-direction to solve for the range.

Question 8

Suppose an object travels with a velocity of 40 m / s at an angle of 75° (relative to the horizontal plane). Which of the following statements is not correct?

Answer 8

t = 1.3s

Question 9

The illustration shows the path of the projectile. Which of the following correctly states the formulas for its motion in two dimensions?

Answer 9

vix = v cos theta
vfx = v sin theta
t = viy/g/2
R = 2v^2(cos theta sin theta)/g = v^2/g sin 2 theta

Question 10

Suppose an object travels with a velocity of 25 m / s at an angle of 30° (relative to the horizontal plane). Which of the following statements about its projectile motion is not correct?

Answer 10

R = 31.875 m