At t = 0 seconds, a bicyclist's velocity was 9 m/s, north. At t = 3 seconds, his velocity was 0 m/s, north.

Question

At t = 0 seconds, a bicyclist's velocity was 9 m/s, north. At t = 3 seconds, his velocity was 0 m/s, north.

What was the bicyclist's acceleration?

A. -3 m/s2, north

B. 0 m/s2, north

C. 9 m/s2, north

D. 27 m/s2, north

I think the answer is A

Answer 1

At t = 0 seconds, a bicyclist's velocity was 9 m/s, north. At t = 3 seconds, his velocity was 0 m/s, north. What was the bicyclist's acceleration?

(A) -3 m/s², north,         (B) 0 m/s², north,           (C) 9 m/s², north,           (D) 27 m/s², north

Detailed Solution:

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Given - Initial Velocity: v_i = 9 m/s (north), Final Velocity: v_f = 0 m/s (north), Initial Time: t_i = 0 s, Final Time: t_f = 3 s

Acceleration = (Change in Velocity)/(Change in Time)

a = Δv/Δt = (v_f − v_i)/(t_f − t_i) = (0 − 9)/(3 − 0) = − 9/3 = − 3 m/s², north <== (A)

Answer 2

We can calculate acceleration by dividing the change in velocity by the amount of time:

a = v_f - v_i / t

where v_f = final velocity and v_i = initial velocity

a = 0 m/sec N - 9 m/sec N / 3 sec

So a = -9 / 3 = -3 meters per second per second north

The negative magnitude of acceleration here indicates that the object was slowing down.