Page 13 - Pra U STPM 2021 Penggal 1 - Physics

Physics Term 1 STPM Chapter 2 Kinematics

(c) Velocity, v

+

0 t t t Time, t
1 2 3
2 –

(d) (i) Neglecting air resistance, the time taken to reach the highest point is given by
v = u + at v = 0, a = –g
0 = u – gt
u
Time taken, t =
g
With air resistance, the retardation a 1 > g
using v = u + at
0 = u – a 1 t 1
u
u
Time taken, t 1 = < (a 1 > g)
a 1 g
Hence, the time taken is shorter.
(ii) Without air resistance, the greatest height reached = H
At the greatest height, v = 0
Using v = u + 2as
2
2
0 = u – 2gH a = –g
2
Greatest height, H = u 2
2g
With air resistance retardation a 1 > g.
u 2 u 2
Hence, the greatest height, H 1 = < (a 1 > g)
a 1 g
Therefore, the greatest height reached is lower.

(e) When the ball moves up, When the ball falls,
initial velocity = u, initial velocity = 0,
final velocity = 0, final velocity, v < u velocity of projection because of friction
time = t u time = t d
1 1
Using s = (u + v)t using s = (u + v)t
2 2
1 1

H 1 = (u + 0)t u
2 H 1 = (0 + v)t d
2
2H 1 2H 1
t u = t d = > t u (v < u)
u v
Hence, the time taken to come down is greater than the time taken to move up.

42

02 STPM PHY T1.indd 42 4/9/18 8:19 AM