Chapter 1-O-level Phy-Part 2 of 4

2.Speed

Speed-distance travelled per unit time

Speed= Distance/time taken ( SI units: m/s )..........EQUATION 1

Equation 1 can ONLY be used in cases where the body is moving with constant speed.

e.g
A car moves at 5 m/s for half an hour.What is the distance travelled?

Solution: Distance= speed*time = 5*(30*60) = 9000 m

3.AVERAGE SPEED

Average speed = Total dist/total time taken

Units are still m/s

DEFINITONS:
SPEED: distance travelled per unit time
VELOCITY : rate of change of displacement
ACCELERATION : rate of change of velocity ( SI units: m/(s*s)

CASE STUDY:

Theory: A body is said to move with uniform velocity if it covers equal distances in equal time intervals while travelling along a straight line and in a specified direction.

Problem:A car moves in a circular path at a constant speed at 10 m/s.What is its acceleration?

Solution : Speed remains constant but the velocity changes continuously because the direction of motion is changing continuously.

EQUATIONS OF MOTION FOR BODY MOVING WITH UNIFORM ACCELERATION:
v= u + at
s= ut + 0.5a(t*t)
(v*v) = (u*u) + 2as
s = 0.5t( u+v)

NOTE: -ve acceleration implies that body is decelerating or undergoing retardation.

example:
A car travels at 25 m/s.Driver suddenly applies brakes and car is brought to rest with uniform deceleration of 4 m/(s*s).
Calculate time taken for car to come to rest.

Use v= u + at

t = (v-u)/a = (0-25)/-4 = 6.25 s


Coming next...speed time graphs....!