TUTORIAL DP014 CHAPTER 4 20_21

TOPIC 5 DP014 SES 2020/2021

TOPIC 4 : FORCES TUTORIAL 5: WORK, ENERGY AND POWER

Learning Outcomes; OBJECTIVE QUESTION

4.1 Basics of Forces and Free Body Diagram 1. Newton’s First Law of motion is consistent with the
a) Identify the forces acting on a body in concept of
different situations: A. Force
i. Weight B. inertia
ii. Tension C. Momentum
iii. Normal Forces D. Impulse
iv. Friction
v. External Forces (pull or push) 2. Which direction does friction travel
A. The same direction as your body
b) Sketch free body diagram. B. The opposite direction as your body
c) Determine static and kinetic friction. C. From the side
D. Upwards, from your feet.
fs  sN
fk  k N 3. Two wooden blocks Q and R of masses 2.0 kg and 1.5
kg respectively are on smooth table as shown in
4.2 Newton’s Law of Motion FIGURE 3 . A force of 7.0 N acts on the block Q so
a) State Newton’s Law of motion. that both the blocks accelerate together
b) Apply Newton’s Law of motion.
7.0 N Q R
2.0 kg 1.5 kg

2.0 kg

FIGURE 1

What is the horizontal force that Q exerted on R?

A. 1.0 N
B. 3.0 N
C. 4.0 N
D. 7.0 N

SUBJECTIVE QUESTION

1. a) State Newton’s First Law.
b) Calculate the magnitude and direction of a force that
balance the three forces acting on particle A as shown
in FIGURE 2.

F2 20N F1 12N

30.0 55.0

45.0 A

F3 30N FIGURE
5

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TOPIC 5 DP014 SES 2020/2021

[Ans:31.7 N, 2.49⁰] 3. a) Distinguish between static and kinetic friction.

2. Based on FIGURE 3 and FIGURE 4. Identify the forces b) FIGURE 6 shows a block of mass m1=6.0 kg on a
and sketch free body diagrams for the block in each horizontal surface with coefficient of kinetic
system. friction, k=0.22 is connected by a string through a
pulley to another block of mass m2 = 3.0 kg. The
(a) v system is released from rest.

Rough Surface i. Sketch the forces acting on the blocks
when they are in motion.
FIGURE 3
ii. Calculate the acceleration of the blocks.
(b) A
m1

m2

Rough Surface FIGURE 6
FIFGIGURUER4E.24 [1.83 ms-2, 23.88 N]

5.

B a) State Newton’s Second Law.

b) A 2.0 kg object is placed on a rough plane

6. A man pulls a 45 kg block at a constant velocity inclined at 30° with the horizontal as shown in
on a rough surface as shown in FIGURE 5. The
angle between the rope and the horizontal is 30 FIGURE 7. It is released from rest and accelerates
and the coefficient of kinetic friction between the
block and the surface is 0.6. at 4.0 m s-2. Calculate the frictional force acting on

(a) Sketch and label all the forces acting on the object.
the block.
2kg
(b) Calculate the tension in the rope.
33000°

FIGURE 7

30 [1.81 N]

FIGURE 5 6. Three wooden blocks connected by a rope of negligible
mass are being dragged by a horizontal force, F in
FIGURE 8.

[227 N] F Mm T m T m

M1 1 2 3

2

1

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TOPIC 5 DP014 SES 2020/2021

FIGURE 8 f
o
Suppose that F = 1000 N, m1 = 3 kg, m2 = 15 kg r
and m3 = 30 kg. Determine A
B
a) the acceleration of the blocks system. ,
a
b) the tension of the rope, T1 and T2.
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(Neglect the friction between the floor and the
wooden blocks.)

(Ans: 20.8 ms-2 T1 =936 N, T2 =624 N)

7.
a) State Newton’s Third Law.
b) Two blocks, A and B of masses 10 kg and 30
kg respectively are placed side by side and in
contact with each another. They are pushed
along a smooth floor under the action of a
constant force F of magnitude 200 N applied
to A as shown in FIGURE 9. Determine
i. the acceleration of the blocks,
ii. the force exerted by A on B.

 AB
F

FIGURE 9

[5ms2, 150 N]