Question

A quantity is measured to be - 30m/sec. is it a speed or velocity? give reason.

Answer 1

it is velocity because velocity is a vector quantity which can be negative or positive
speed is a scalar quantity which is always positive

Answer 2

answer : velocity

before answering, we should understand what is the meaning of velocity while what is the meaning of speed?

velocity is the rate of change of displacement with respect to time. or, in simple way, velocity = displacement/time taken.

but you already know, displacement maybe negative , zero or positive.

so, velocity also maybe negative , zero or positive.

speed is the rate of change of distance with respect to time. and we know, distance can't be negative. so, speed must be positive.

given, A quantity is measured to be -30m/s ( a negative value). from above explanation it is clear that it must be velocity.