Question

a train approaches a rail yard with a velocity of 20 m/s w. after 35 s, the train has a velocity of 7.0 m/s w. what is the average acceleration of the train?
(a) $0.37\text{m/s}^2$ w (b) $0.37 \text{m/s}^2$ e
(c) $0.26 \text{m/s}^2$ w (d) $0.26 \text{m/s}^2$ e
a
b
c
d

Explanation:

Step1: Define variables and formula

Let west be positive. Average acceleration formula:
$$a_{avg} = \frac{v_f - v_i}{\Delta t}$$
Where $v_f=7.0\ \text{m/s}$, $v_i=20\ \text{m/s}$, $\Delta t=35\ \text{s}$

Step2: Substitute values into formula

$$a_{avg} = \frac{7.0 - 20}{35}$$

Step3: Calculate acceleration value

$$a_{avg} = \frac{-13}{35} \approx -0.37\ \text{m/s}^2$$
The negative sign means direction is east.

Answer:

(b) 0.37 m/s² [E]