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⚙️AP Physics C: Mechanics
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⚙️AP Physics C: Mechanics

FRQ 2 – Translation Between Representations
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Unit 1: Kinematics
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Practice FRQ 1 of 151/15

2. A ball is launched from the ground at time t=0t = 0t=0 with an initial speed of v0=10.0v_0 = 10.0v0​=10.0 m/s at an angle of θ=37°\theta = 37°θ=37° above the horizontal, as shown in Figure 1. Air resistance is negligible, and the acceleration due to gravity is g=10g = 10g=10 m/s². The ball reaches its maximum height at time t1=0.60t_1 = 0.60t1​=0.60 s and lands on the ground at time tf=1.2t_f = 1.2tf​=1.2 s.

Figure 1. Projectile launched from ground with initial speed v₀ = 10.0 m/s at θ = 37° above the horizontal (ground frame axes shown).

Figure 1

Figure 2. Axes for graphing the vertical velocity component vᵧ as a function of time t from 0 to 1.2 s.

Figure 2
A.

On the axes in Figure 2, sketch a graph of the vertical component of the ball's velocity vyv_yvy​ as a function of time ttt for the entire flight from t=0t = 0t=0 to t=1.2t = 1.2t=1.2 s. The graph should show correct initial and final values, and the value at maximum height.

B.

Derive an expression for the magnitude of the ball's displacement from its launch point to its position at t=0.30t = 0.30t=0.30 s. Express your answer in terms of x1x_1x1​, y1y_1y1​, and physical constants, as appropriate. Begin your derivation by writing a fundamental physics principle or an equation from the reference information. Calculate a numerical value for the displacement. At time t=0.30t = 0.30t=0.30 s, the ball is at position (x1,y1)(x_1, y_1)(x1​,y1​) where x1=2.4x_1 = 2.4x1​=2.4 m and y1=1.35y_1 = 1.35y1​=1.35 m.

Figure 3. Coordinate system for drawing the ball’s velocity vector v and acceleration vector a at t = 0.90 s.

Figure 3
C.

On the coordinate system in Figure 3, draw and label two vectors: At time t=0.90t = 0.90t=0.90 s, the ball is descending toward the ground.

  • The velocity vector v⃗\vec{v}v of the ball at t=0.90t = 0.90t=0.90 s
  • The acceleration vector a⃗\vec{a}a of the ball at t=0.90t = 0.90t=0.90 s

The vectors should have correct directions and magnitudes relative to each other. Each vector should be clearly labeled.

Figure 4. Ground-frame view: a cart moves right at constant speed v_cart = 6.0 m/s while the ball follows a projectile path (air resistance negligible).

Figure 4
D.

Describe how one component of the ball's velocity as measured by the observer on the cart differs from that component as measured by an observer on the ground. Specify which component (horizontal or vertical) you are describing and state whether its magnitude is greater than, less than, or equal to the magnitude measured from the ground. An observer stands on a cart that moves to the right with a constant velocity of vcart=6.0v_{cart} = 6.0vcart​=6.0 m/s, as shown in Figure 4. The cart begins moving at t=0t = 0t=0, at the same instant the ball is launched. The ball is launched from a position directly beside the cart.

Justify your answer using principles of relative motion.

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Free Response Question Practice

This practice environment simulates the AP AP Physics C: Mechanics Free Response Questions section. Here are some guidelines:

  • Read each question carefully before responding. Pay attention to command verbs like "identify," "explain," "analyze," or "evaluate."
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Tip: Answer all parts of each question. Partial credit is often available, so even if you are unsure, provide what you know.