Question

(a) Define velocity. What is the SI unit of velocity?
(b) What is the difference between speed and velocity?
(c) Convert a speed of 54 km/h into m/s.

Answer 1

(a) The rate of change of displacement is known as the velocity. It can be calculated by obtaining the ratio of displacement and the total time taken. The SI unit of velocity is 'm/s', same as of the speed.

(b) Speed is the rate of change of distance travelled by a body whereas velocity is the rate of change of displacement by the body. Speed is a directionless quantity but the velocity is a vector quantity, we need magnitude as well as direction to describe it.

(c) Given speed, v = 54 km/h

1 km = 1000 m

1 h = 3600 s

So, $v=54\frac{\mathrm{km}}{\mathrm{h}}=54\times \frac{1000\mathrm{m}}{3600\mathrm{s}}=\frac{540}{36}\mathrm{m}/\mathrm{s}$

$\therefore v=54\mathrm{km}/\mathrm{h}=15\mathrm{m}/\mathrm{s}$