Question

• What happens to the acceleration of a system when the mass of the system increases if the force stays constant?
• What happens to the speed when the force increases but the mass stays constant?
• You double the force on a system but the acceleration is still the same. What must have happened to the mass?
• What does μ represent? What are its units?
• Which surface would you expect to have the larger coefficient of friction, ice or asphalt? Why?
• What is the normal force? How can you balance the normal force?
• If the coefficient of friction between two surfaces is 0.2, and the normal force is 20N, what is the value
  of the friction force?
• Why is it harder to move an object up an incline at an angle of 80 degrees versus an angle of 20
  degrees?

Answer 1

1. From Newton's second law we know that

if we increase the mass of the system by keeping force constant, the acceleration decreases.

2. If you are talking about the speed of a particle at a given instant, then when we apply a force F, the acceleration is given by

Velocity at time t is given by

When at time t, for force F the velocity is v. Now if I double the force, then the velocity is

So if we increase the force, the velocity at a given instant also increases. Also the speed.

3. When you double the force if acceleration remains same, then it means the mass of the object has also been doubled. This is evident from Newton's second law written above.

4. is coefficient of friction. It has no units.

5. Asphalt has larger coefficient of friction compared to ice. Because the ice is a smooth surface where as Asphalt is a rough surface.

6. The frictional force is given by

This is the frictional force.

7. The component of gravitational force along the incline is given by

For 20 degrees

If we want to move an object up the incline, we must exert force against the gravitational force component along the incline. When it 80 Degree, the component of force is greater compared to 20 Degree. That's the reason why it is harder to move the object up the incline when the angle is 80 compared to 20 degrees.