Question

1. give an example of an isolated system.

a. a cyclist moving along a rough road
b. a figure skater gliding in a straight line on an ice rink
c. a baseball player hitting a home run
d. a man drawing water from a well
8.3 elastic and inelastic collisions

1. in which type of collision is kinetic energy conserved?

a. elastic
b. inelastic

1. in physics, what are structureless particles that cannot rotate or spin called?

a. elastic particles
b. point masses
c. rigid masses

1. two objects having equal masses and velocities collide with each other and come to a rest. what type of a collision is this and why?

a. elastic collision, because internal kinetic energy is conserved

Explanation:

• Question 26: An isolated system is one where there is no exchange of matter or energy with the surroundings. A figure skater gliding in a straight line on an ice rink (assuming no friction, air - resistance etc. for the sake of the example) is a better approximation of an isolated system compared to the other options. A cyclist on a rough road has frictional forces (energy loss), a baseball player hitting a ball has external forces (from the bat), and a man drawing water has work done against gravity (energy exchange).
• Question 27: In an elastic collision, kinetic energy is conserved. In an inelastic collision, kinetic energy is not conserved (some is converted into other forms like heat, sound, or deformation energy).
• Question 28: Point masses are structureless particles that cannot rotate or spin. Elastic particles relate to collision properties, and rigid masses are not the standard term for non - rotating/non - spinning structureless particles.
• Question 29: When two objects with equal masses and velocities collide and come to rest, kinetic energy is not conserved (it was non - zero before and zero after). So, it is an inelastic collision. In an elastic collision, kinetic energy is conserved.

Answer:

• 26. b. A figure skater gliding in a straight line on an ice rink
• 27. a. Elastic
• 28. b. Point masses
• 29. Not an elastic collision (so options other than a). It is an inelastic collision because kinetic energy is not conserved (initial kinetic energy \(K_{i}=\frac{1}{2}mv^{2}+\frac{1}{2}mv^{2}=mv^{2}\) and final kinetic energy \(K_{f} = 0\))