Question

1. You slide an object across a horizontal surface, that object will eventually slow down and stop. What’s causing this and why?

2. Name two instances in your daily life where “conservation of energy” plays a role.

3. In a very general sense, if one object hits another that is stationary, how does the collision’s type (elastic vs. inelastic) affect the energy of the objects?

4. When opening a door, it is easier to do so by pushing on the doorknob, far from the hinges. Why?

5. Why can a molecule with three atoms store more energy than a molecule made of only one atom?

Answer 1

1: When an object slides across a horizontal surface, the friction force tries to drags that object behind and this force works constantly on that body hence eventually the momentum of the body under the influence of this friction becomes zero and tha object stops.

2: When we use electric motor, the motor changes the electrical energy into mechanical energy. But the energy remains conserved.

When we play marbles, which are perfectly elastic then in collision of two marbles energy remains conserved.

3: If the collision is elastic the energy of the system remains conserved

If collision is not elastic then some energy is lost to other forms of energy e.g. heat energy, vibration energy etc.

4: It is easier to open the door pushing it far from nob because the rotational force F = mv²/R is inversely proportional to R that means as R(distance from door nob) increase the force decrease.

5: According to equipartition of energy theorem,

The energy associated with each molecule of gas is given by

E= fNKT/2

Where f= degrees of freedom

Since triatomic molecules will have 9 degrees of freedom in compare of monoatomic molecules which have only three, they will have more energy associated with each molecule.