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Physics Form 4 Chapter 2 Force and Motion I

EXAMPLE 2.8

Sometimes there are too few ticks to be cut into Solution
strips. In such cases, direct analysis is needed to Average initial velocity, u = 0.6 cm
determine the acceleration. The following ticker 0.02 s
tape shows the motion of a trolley. The ticker = 30 cm s –1
timer vibrates at a frequency of 50 Hz. 1.6 cm
Average final velocity, v = 0.02 s
Initial Final –1
= 80 cm s

Time taken, t = (11 – 1) × 0.02 s
Uniform acceleration = 0.2 s
0.6 cm 1.6 cm v – u Chapter
Figure 2.19 Therefore, acceleration, a = t
80 – 30
= 0.2 2
= 250 cm s –2

Determining Acceleration with Photogate and Electronic Timer

A pair of photogates A and B is Photogate and electronic x cm
arranged at two different locations timer system 0000 A
along an inclined plane. This type B Cardboard
of photogate consists of optical Trolley
sensors that can measure the time,
t, taken by an object passing
through it. In this case, the object Inclined plane
is a cardboard with a length of x cm
attached to the top portion of a
trolley. Figure 2.20
x
1. Average initial velocity, u, when the cardboard passes through photogate A is where t A is the time
taken by the cardboard to pass through photogate A. t A
x
2. Average final velocity, v, when the cardboard passes through photogate B is where t B is the time
taken by the cardboard to pass through photogate B. t B

3. The time taken for the trolley to move between photogate A and photogate B, t, can be measured by
the time difference recorded when the trolley moved between photogate A and photogate B.

Results
x x
u = dan v =
t A t B
Therefore, the acceleration, a, is given by the following:
x x
v – u t B – t A
a = = cm s –2
t t
This value can be divided by 100 to convert to the unit m s .
–2

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