To determine the velocity of an object that starts from rest and experiences a constant acceleration, we can use one of the fundamental equations of motion. The equation we will use is: \[ v = u + at \] Where: - \( v \) is the final velocity, - \( u \) is the initial velocity, - \( a \) is the acceleration, - \( t \) is the time. ### Step-by-Step Explanation 1. **Identify the Initial Conditions**: - The object starts from rest, which means the initial velocity \( u = 0 \) m/s. - The acceleration \( a = 4 \) m/s² (given). - The time \( t = 5 \) seconds (given). 2. **Substitute the Values into the Equation**: We can now substitute the known values into the equation: \[ v = 0 + (4 \, \text{m/s}^2)(5 \, \text{s}) \] 3. **Perform the Calculation**: - First, calculate the product of acceleration and time: \[ 4 \, \text{m/s}^2 \times 5 \, \text{s} = 20 \, \text{m/s} \] - Now, substitute this back into the equation for \( v \): \[ v = 0 + 20 \, \text{m/s} = 20 \, \text{m/s} \] 4. **Final Answer**: The final velocity of the object after 5 seconds is \( 20 \, \text{m/s} \). ### Why the Correct Option is C (20 m/s) The calculations show that after 5 seconds of constant acceleration at 4 m/s², the object reaches a velocity of 20 m/s. This is consistent with the physics of motion under constant acceleration, confirming that option C is indeed correct. ### Explanation of Other Options - **Option A (10 m/s)**: This option is incorrect because it suggests that the object would only reach half the calculated velocity after 5 seconds. Given the acceleration of 4 m/s², the object would not reach this speed in the given time. - **Option B (15 m/s)**: This option is also incorrect. It implies that the object would have a velocity of 15 m/s after 5 seconds, which does not align with the calculated result of 20 m/s based on the acceleration provided. - **Option D (25 m/s)**: This option is incorrect as well. It suggests that the object would exceed the calculated velocity. Given the acceleration and time, the object cannot reach this speed. ### Common Pitfalls - **Misunderstanding Initial Velocity**: Remember that starting from rest means the initial velocity is zero. If you mistakenly assume a non-zero initial velocity, it will lead to incorrect calculations. - **Forgetting to Use the Correct Formula**: Ensure you are using the correct equation of motion for constant acceleration. The equation \( v = u + at \) is specifically designed for this scenario. ### Revision Summary - Use the equation \( v = u + at \) to find final velocity under constant acceleration. - Ensure to correctly identify initial conditions: starting from rest means \( u = 0 \). - Substitute values carefully and perform calculations step-by-step. - Double-check your final answer against the options provided to ensure accuracy. By following these steps and understanding the underlying principles, you can confidently solve similar problems involving constant acceleration in the future.