Question

a car travels at 15 m/s for 10 s. it then speeds up with a constant acceleration of 2.0 m/s2 for 15 s. at the end of this time, what is its velocity?
15 m/s
30 m/s
45 m/s
375 m/s

Explanation:

Step1: Identify initial velocity and acceleration phase

The car's initial velocity \( u = 15 \, \text{m/s} \) (during the first 10 s, but we care about the velocity before acceleration starts, which is 15 m/s). Then it accelerates with \( a = 2.0 \, \text{m/s}^2 \) for \( t = 15 \, \text{s} \).

Step2: Use the kinematic equation \( v = u + at \)

We use the equation for final velocity under constant acceleration: \( v = u + at \). Substitute \( u = 15 \, \text{m/s} \), \( a = 2.0 \, \text{m/s}^2 \), and \( t = 15 \, \text{s} \).

$$ v = 15 + (2.0 \times 15) $$

Step3: Calculate the value

First, calculate \( 2.0 \times 15 = 30 \). Then add to initial velocity: \( 15 + 30 = 45 \, \text{m/s} \).

Answer:

45 m/s (corresponding to the option "45 m/s")