Page 211 - Physics

Work, energy and power

1 1 1 2
(
= mv − mu 2 = × 0.012 kg × 320 m / s)
2
2 2 2
(
1 2 .  614.4 kgm /s  2 2 614.4 J .
2
∴ ΔKE = m v − u )
2 Therefore, the kinetic energy of bullet is
614.4 J
Example 9.3
An object has a mass of 5 kg. What is Acti vity 9.1
its kinetic energy if its speed is:
(a) 5 m/s? Aim: To investigate the
(b) 10 m/s? relationship between
Solution work and kinetic energy.
Given that: mass (m) = 5 kg and Materials: Wooden block, PVC tube,
speed (v) = 5 m/s and 10 m/s.. metre rule and metal ball

1
(a) KE = mv 2 Procedure
2 1. Place one end of a PVC tube about
1 2 1 m long on a wall while the other
(
= ×5 kg × 5 m / s)
2 end rests on a smooth table.
= 62.5 kgm /s = 62.5 J . 2. Using a metre rule measure
2
2
perpendicular height (h) from the
1
(b) KE = mv 2 table to the point where the PVC
2 tube rests on the wall. Record the
1 2 value of h (start with h = 100 cm).
(
KE = ×5 kg × 10 m / s)
2 3. Place the wooden block as shown in
2
2
! 250 kgm /s ! 250 J Figure 9.11.
Ruler
KE = 250 J. Ruler
Comparing the two examples, it shows PVC tube
PVC tube
that, if the speed of an object is doubled, its
kinetic energy increases by a factor of 4. Wooden block h h
Wooden block
Example 9.4

What is the kinetic energy of a 12 g bullet
travelling at the speed of 320 m/s?

Solution
Given that mass (m)=12 g = 0.012 kg, Figure 9.11
speed (v) = 320 m/s. 4. Release the metal ball from the upper
1 end of the wall, so it rolls inside the
KE = mv 2 tube towards the lower end.
2

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Physics Form 1 Final.indd 205 16/10/2024 20:58