CBSE Class 9 Answered

lakhmir singh an manjit kaur

page 42 question no 48

a motorcycle is being driven at a speed of 20 m/s when brakes are applied to bring it to rest in 5 seconds the deceleration produced in this case will be

a ) +4m/s^2 b) -4 m/s^2 c) +0.25m/s^2 d) -0.25m/s^2

my solution is  a = (v-u)/t

v=0 u = 20 m/s t = 5 s

hence  a = acceleration = (0-20)/5

i.e. my answer is -4 m/s^2

but answer  given in book is +4 m/s^2

pl tell me why my answer is wrong as per my knowledge deceleration means negative acceleration so answer  how can be in + sign