• Discuss Newton's three Laws of Motion.
• Calculate the forces for a system in equilibrium.
• Calculate static and kinetic frictional forces.

Conceptual Questions

1. If an object is at rest, can we conclude that no external forces are acting on it?
2. How much does an astronaut weigh out in space, far from any planets?
3. If a car is traveling westward at a constant speed of 20 m/s, what is the resultant force acting on it?
4. In a tug-of-war between two athletes, each pulls on the rope with a force of 200 N. What is the tension in the rope?
5. A child in a car holds onto a string attached to a helium-filled balloon. What happens to the balloon when the car accelerates forward?
6. Can an object be in equilibrium if only one force acts on it?

 Problems

1. A 6.0-kg object undergoes an acceleration of 2.0 m/s². a) What is the magnitude of the resultant force acting on it? b) If this same force is applied to a 4.0-kg object, what acceleration is produced?
2. After falling from rest from a height of 30 m, a .50-kg ball rebounds upward, reaching a height of 20 m.  If the contact between ball and ground lasted 2.0 ms, what average force was exerted on the ball?
3. An object with mass m₁ = 5.00 kg rests on a frictionless horizontal table and is connected to a cable that passes over a pulley and is then fastened to a hanging object with mass m₂ = 10.0 kg.  Find the acceleration of each object and the tension in the cable.
4. A hockey puck is hit on a frozen lake and starts moving with a speed of 12.0 m/s.  Five seconds later, its speed is 6.00 m/s. a) What is its average acceleration? b) What is the average value of the coefficient of kinetic friction between puck and ice? c) How far does the puck travel during the 5.00-s interval?