Tuesday, October 20, 2009

The Equation of linear motion

The equations of linear motion is apply to bodies moving linearly with uniform acceleration .
There are 5 variables in the equation
v = final velocity,
= initial velocity,
s = displacement,
a = acceleration,
= time

You should be able to solve problems using equation about.

Example :
1. A cyclist accelerates uniformly at 1.2 ms-2 in 10 s from rest. What is his displacement at this time?

  • Rest mean zero velocity !!
  • You need to know 3 variables to find out the required quantities .
Suggested solution

u = 0 ms-1
a = 1.2 ms-2
t = 10 s
v = ? ( since v is not given you are unable to calculate s using equation 1, 2, 4 and 5)

substitute all given information into equation 3
s= ut+ 1/2 at
s= (0) (10) + 1/2 (1.2) (10)2
=60 m (very often, student forget to mention the unit. )

2. A car approaches a traffic light at 15m/s. The traffic light turns red and the driver applies the brakes at the distance of 25 m from the junction and decelerate at 5 ms-2. Can the car come to complete stop before reaching the stop line at the traffic light? (ans : yes)

  • remember to insert the negative sign (-) for decelerate

*learn more in http://en.wikipedia.org/wiki/Equations_of_motion


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