Question

A 6.0 kg ball moving at 5.0 m/s hits a 5.0 kg putty at rest and sticks to it. The resulting ball+putty moves at 3.0 m/s. (a) What is the kinetic energy of the ball before it hits the putty? (b) What is the kinetic energy of the putty before it gets hit the ball? (c) What is the kinetic energy of the ball+putty after the collision? (d) Is the Kinetic Energy conserved in this collision? Explain your reasoning.

Answer 1

Given:

A 6.0 kg ball moving at 5.0 m/s hits a 5.0 kg putty at rest and sticks to it. The resulting ball+putty moves at 3.0 m/s.

To find:

• KE of ball before hitting putty?
• KE of putty before hitting ball?
• KE of ball+putty after collision?

Calculation:

KE of ball before hitting putty:

$KE = \dfrac{1}{2} m {v}^{2}$

$\implies \: KE = \dfrac{1}{2} \times 6 \times {(5)}^{2}$

$\implies \: KE = 75 \: joule$

KE of putty before hitting ball:

$KE = \dfrac{1}{2} m {v}^{2}$

$\implies \: KE = \dfrac{1}{2} \times 5\times {(0)}^{2}$

$\implies \: KE = 0 \: joule$

KE of ball-putty system:

$KE = \dfrac{1}{2} M {v}^{2}$

$\implies \: KE = \dfrac{1}{2} \times (6 + 5)\times {(3)}^{2}$

$\implies \: KE = \dfrac{1}{2} \times 11\times {(3)}^{2}$

$\implies \: KE = 49.5 \: joule$

Kinetic energy (in this case) will not be conserved because a part of the kinetic energy will be converted to other forms of energy like heat and radiation during collision.

Hope It Helps.