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6 votes
6 votes
A 2kg mass is moving at 3m/s. What is its kinetic energy?

User Edward Lee
by
2.8k points

2 Answers

24 votes
24 votes

Answer:

7.2

J

or

80

%

of the original kinetic energy is lost.

Step-by-step explanation:

Take A Ball For an Example.

Conservation of momentum says that momentum before a reaction and momentum after a reaction must be equal.

Momentum is the product of mass and velocity, so

(

m

v

)

1

=

(

m

v

)

2

Only moving objects have momentum, so all the momentum beforehand is in the moving ball, so

(

m

v

)

1

=

2

k

g

×

3

m

s

1

=

6

N

s

This ball stops moving, and now only the

10

k

g

ball moves, so momentum after the reaction is

(

m

v

)

2

=

10

k

g

×

v

m

s

1

We know that this is equal to the momentum before, so

10

×

v

=

6

v

=

0.6

m

s

1

Now for the second part. Calculating kinetic energy is done by the equation

E

=

1

2

m

v

2

which, before the reaction, is

E

=

1

2

×

2

×

3

2

=

9

J

after the reaction, it will be

E

=

1

2

×

10

×

0.6

2

=

1.8

J

Overall, then, the kinetic energy lost is

Δ

E

=

9

1.8

=

7.2

J

or, as a percentage,

9

1.8

9

×

100

%

=

80

%

of the kinetic energy is lost.

I Hope This Helps.

User Geanine
by
2.3k points
8 votes
8 votes

Step-by-step explanation:


(1)/(2)m {v}^(2) \\ (1)/(2) * 2 * {3}^(2) \\ 1 * 9 = 9j

User Murilo Vasconcelos
by
2.6k points