Page 32 - Physics Form 5 KSSM_Neat

Example 2

Figure 1.28 shows a box of weight 50 N stationary on an inclined plane.
(a) Draw a free body diagram of the box showing the weight of the
box, W, normal reaction, R and the frictional force, F .
R
(b) By drawing a scaled triangle of forces diagram, determine
KEMENTERIAN PENDIDIKAN MALAYSIA
the magnitudes of the normal reaction, R and the frictional
force, F . 40°
R
(c) By resolving the weight of the box, W into a component Figure 1.28
parallel to the inclined plane and a component perpendicular
to the inclined plane, determine the magnitudes of the
R
normal reaction, R and the frictional force, F . F
R R
Solution

(a) Figure 1.29 shows the free body diagram of the box. 40°
(b) Scale: 1 cm = 10 N W
Figure 1.29

Step 1: Step 2: Step 3: Step 4:
Draw the line AB Mark the angle 40° and Mark the angle 40° Complete the
of length 5.0 cm draw the line BC to and draw the line triangle ABD with
to represent the show the direction of AD to represent the direction of forces.
weight, W. force, F . force, R.
R
1 2 3 4
A A A A
40° 40°

R R

W W W W
C C
D D

F F
R R F R
B 40° B 40° B B

Step 5:
Measure the length of the BD = 3.2 cm
F = 3.2 × 10
side BD, which represents the 123 R
force, F . = 32 N
R
Step 6: AD = 3.8 cm
Measure the length of the 123
R = 3.8 × 10
side AD, which represents the = 38 N
force, R.

22 LS 1.3.3