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Chapter 2

Forces And Motion

6

Linear Motion (I) Distance And Displacement Distance: a scalar quantity. Displacement: a vector quantity.

Town B Displacement of town B from town A = 500 km

Displacement is distance travelled in a specific direction.

Speed: a scalar quantity. Velocity: a vector quantity. 2 m s–1 C

B

2 m s–1 String

A

Distance of town B from town A = 620 km

Town A

Speed And Velocity

An object is moving with a constant speed of 2 m s–1 in a circle. It has a different velocity at different points along the circle. The direction and hence the velocity of the object is always changing. Velocity,

2 m s–1 D

2 m s–1

where s is the displacement t is the time taken

Acceleration = Rate of change of velocity a=

v–u t

where v is the final velocity u is the initial velocity t is the time taken

s v= t

Equations of Linear Motion with Uniform Acceleration: u–v s= t 2 v = u + at s = ut + 1 at 2 2 v2 = u2 + 2as

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Question An object accelerates uniformly along a straight line from a velocity of 5 m s–1 to 25 m s–1 in 4 s. Calculate (a) the acceleration and (b) the total displacement travelled by the object. Solution v–u 25 – 5 (a) Acceleration a = t = = 5 m s–2 4 1 1 (b) Total displacement s = ut + at2 = 5 × 4 + × 5 × 42 = 60 m 2 2 © Marshall Cavendish ( Malaysia ) Sdn. Bhd.