Page 56 - text book form physics kssm 2020

Solving Problems Related to Free Falling Objects

Objects thrown vertically upwards or released and falls
downwards experience gravitational acceleration, g. Therefore, Object thrown Assumption:
the equations of linear motion below can be applied to free upwards Motion in the
falling objects. positive direction

1
v = u + gt s = ut + gt 2 v = u + 2gs
2
2
2 Object
In solving problems, our assumptions are upward motion
is motion in the positive direction and downward motion is Assumption:
motion in the negative direction as shown in Figure 2.41. Object released Motion in the
downwards
negative direction

Figure 2.41 Assumption of direction
of an object’s vertical motion

Example 1
SMART
Amirah threw a ball vertically upwards with an initial SMART INFO
–1
velocity of 10 m s . Calculate the:
(a) time for the ball to achieve maximum height Ball moves upwards, u is
(b) maximum height that can be reached by the ball positive but g is negative.
–2
Ignore air resistance. [g = 9.81 m s ]
Solution:

(a) Step Initial velocity , u = 10 m s –1
Final velocity at maximum height, v = 0 m s –1
List the given information in –2
symbols. Acceleration, g = –9.81 m s
123
Step
v = u + gt
Identify and write down the
formula used.
123
Step 0 = 10 – 9.81t SMART INFO
SMART
Substitute numerical values into 123 t = 10
the formula and perform the 9.81 1 2
calculations. = 1.02 s The equation s = ut + gt
2
can also be used.
1
(b) v = u + 2gs s = ut + gt 2
2
2
2
1
0 = 10 + 2(–9.81)s = 10(1.02) + (–9.81)(1.02) 2
2
10 2 = 5.10 m 2
s =
2 × 9.81
= 5.10 m
50
50 2.3.2 2.3.3
2.3.3
2.3.2