Page 16 - Pra U STPM 2021 Penggal 1 - Physics

Physics Term 1 STPM Chapter 2 Kinematics

2.2 Projectile
2008/P2/Q1, 2013/P1/Q2, 2014/P1/Q16
Learning Outcomes

Students should be able to:
• solve problems on projectile motion without air resistance
• explain the effects of air resistance on the motion of bodies in air
2
1. A projectile is a body that travels under the action of gravity after being projected at an angle to the
horizontal.
2. The motion of a projectile consists of two components:
(a) a vertical component which is motion with uniform acceleration, g the acceleration due to
gravity,
(b) a horizontal component which is motion with constant velocity.
3. The path of a projectile is a curve known as parabola.

10 m s –1 30 m s –1
20 m s –1 30 m s –1
30 m s –1 –1
30 m s –1 30 m s –1 –10 m s –1 30 m s
–20 m s –1 30 m s –1
–1
40 m s –1 30 m s
–1
50 m s –30 m s –1 –1
53° a = –g 30 m s
30 m s –1 –1 –1
–40 m s 50 m s
Figure 2.6 Projectile
4. Figure 2.6 shows the motion of a tennis ball with an initial velocity of 50 m s at an angle of
–1
projection 53° to the horizontal. An analysis of the motion shows that:
(a) The horizontal component of velocity is constant at 30 m s , because there is no horizontal
–1
force on the ball.
(b) The horizontal displacements are the same for equal time intervals.
(c) The vertical component of velocity continuously changes during the motion.
(d) At the highest point of the trajectory, the vertical component of velocity is zero.
(e) The acceleration a is constant and vertically downwards, a = –g.
5. To study the motion of a projectile, we consider the horizontal component and vertical components
separately.

u sin θ u

a = –g
H
y
θ
O
u cos θ
x
R

Figure 2.7

45

02 STPM PHY T1.indd 45 4/9/18 8:19 AM