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PT HW 3.1

(linear) Kinetic Energy and Wor

1. a. A bicycler has a mass of 80. kg. He pedals the bike 100 min 20 seconds. What is

his kinetic energy (KE; ) ?

Given, Unknown:

Equation, Substitute:

Solution:

1. b. The bicycler (still 80. kg of mass) doubled his speed to 200m in 20 seconds, What

his new kinetic energy (KE) ? What is the ratio of KE; and KE?

Given, Unknown:

Solution

Equation, Substitute:

1. c. The bicycler doubled his speed. What happened to his KE?

2. a. Car A has a mass of 250. kg. It's engine accelerates it from 0.0 to 20. m/s in 6.0

ndo (a) what is the car's acceleration in m s?

tio hstitute:

Solution:

1. a) 1 kJ

1. b) 4 kJ

ratio 1:4

1. c) 4 times as before

2. a) 3.33 m/s2

Explanation:

1. a) bicycle's velocity = Displacement/time

=100/20 m/s

=5 m/s

bicycler's KE = 1/2 * mass * (velocity) ^2

=1/2*80*5^2

=1000 J = 1 kJ

1. b) bicycle's new velocity = 200/20 m/s

=10 m/s

bicycler's new KE = 1/2*80*10^2

=4000 J = 4 kJ

Ratio = KE 1 : KE new

= 1 : 4

1. c) when bicycler's speed was doubled it increased the KE by 4 times (2^2). because In KE we consider the square of the speed, so the factor we increase the speed, the KE will get increased with the square value of it

ex : speed is triple the prior value, then the KE is as 3^2 times as before. that is 9 times

2. a) car acceleration = (20-0) / 6 m/s2

= 3.33 m/s2