Question

What is acceleration? What is the unit of acceleration? Is it vector or scalar?

Answer 1

The acceleration is the vector that is defined as follows:

$$\mathbf{a} = \dfrac{d\mathbf{v}}{dt}$$

where $\mathbf{v}$ is the vector of instantaneous velocity of the object, and the derivative is taken with respect of time. Sice the velocity is a vector, the acceleration is a vector as well.

Since the unit of velocity is m/s, and unit of time is s, the unit of acceleration is

$$m/s/s \space \text{or} \space m/s^2$$

Answer. 1) The first derivative of velocity with respect of time, 2) m/s^2, 3) vector.