Section 6.3 Kinetic Energy (ke)

Section 6.3 Kinetic energy (KE)

© Manhattan Press (H.K.) Ltd.

1

6.3 Kinetic energy (SB p. 129)

Kinetic energy A body possesses kinetic energy when it is moving v=0

v≠ 0 © Manhattan Press (H.K.) Ltd.

KE = 0

KE ≠ 0

2

6.3 Kinetic energy (SB p. 129)

Kinetic energy

By

v2 – u2 = 2as v2 2s a=

By

© Manhattan Press (H.K.) Ltd.

F = ma mv2 F = 2s

∴ Work done gain in KE

=

=W

1 KE = mv2 2

= Fmv × 2s 2 =

3

6.3 Kinetic energy (SB p. 130)

Example 2: In a shot put, a ball of mass 7.26 kg leaves an athlete's hand at a speed of 12 m s−1. If the ball is in contact with the hand for a distance of 1 m, find the average force acting on the ball. Solut Work = Change in kinetic energy ion 1 Fs = 2 mv2 1 F× 1= × 7.26 × (12)2 2

∴ F = 523 N The average force acting on the ball is 523 N. © Manhattan Press (H.K.) Ltd.

4

6.3 Kinetic energy (SB p. 130)

Class Practice 3: A stationary golf ball of mass 0.25 kg is struck with a force of 200 N. If the club is in contact with the ball for a distance of 1 cm, find the speed of the ball when it Ans leaves the club. wer Work = Change in kinetic energy 1 Fs = mv2 2 √(2 × F × s)/m = √(2 × 200 × 0.01)/0.25 = 4 v = ________________________________ 4 m s−1 The speed of the golf ball is ___________________.

© Manhattan Press (H.K.) Ltd.

5

To section 6.4

© Manhattan Press (H.K.) Ltd.

6