Question

Use the table to answer the question.

The table shows the mass and velocity of two objects before and after collision.

Before After
m
1
=
1.0

kg
m
2
=
2.0

kg
m
1
=
1.0

kg
m
2
=
2.0

kg
v
1
=
2.0

m
/
s
v
2
=
−
1

m
/
s
v
1
=
−
2.0

m
/
s
v
2
=
1

m
/
s
Given the data, what is the kinetic energy of the system before and after in this elastic collision?

Answer 1

Kinetic energy before:
KE = 1/2(1.0)(2.0^2) + 1/2(2.0)(-1.0^2) = 0.5·4 + 1·1 = 2.0 + 1.0 = 3.0 J

Kinetic energy after:
KE = 1/2(1.0)(-2.0^2) + 1/2(2.0)(1.0^2) = 0.5·4 + 1·1 = 2.0 + 1.0 = 3.0 J

So KE = 3.0 J both before and after (energy conserved).