Define negative acceleration.

(a) Uniform acceleration and non-uniform acceleration.

Positive acceleration and negative acceleration.

A bus decreases its speed from $80 \mathrm{km}/\mathrm{h}$ to $60 \mathrm{km}/\mathrm{h}$ in $5 \sec$. Find the acceleration of the bus.

 Find the initial velocity of a car which stops in $\mathrm{}$ 10 \sec $$ after applying brakes at the rate of $\mathrm{}$ 2 \mathrm{m}/{\mathrm{s}}^2${\mathrm{}}^{}$. 

A ball initially moving at a speed of $25 \mathrm{m}/\mathrm{s}$ is acted upon by a constant retardation of $2.5 \mathrm{m}/{\mathrm{s}}^2$. For how long will the ball roll, before coming to rest?