Review U2 ANSWERS PDF

Name______________________________ Test Study Guide for Physical Science Test: Unit 2- FORCES Momentum 1. What is the formula for momentum? p= mv 2. What does Conservation of Momentum mean? If 2 objects collide, the momentum before the collision is equal to teh momentum after t...

Name______________________________ Test Study Guide for Physical Science Test: Unit 2- FORCES Momentum 1. What is the formula for momentum? p= mv 2. What does Conservation of Momentum mean? If 2 objects collide, the momentum before the collision is equal to teh momentum after the collision. 3. What is the formula for the conservation of momentum? m1v1 + m2v2 = m1v1 + m2v2 Forces 1. How is force defined? A push or pull 2. What is “net force”? The sum of all forces acting on an object 3. If the net force is 0, what does it mean? The forces acting on the object are balanced, meaning the object is either not moving or moving with constant velocity 4. If the net force is not 0 what does it mean? The forces acting on the object are unbalanced, meaning the object is accelerating 5. What is the result of balance forces on an object? object is either not moving or moving with constant velocity 6. What is the result of an unbalanced force on an object? the object is accelerating 7. State the metric unit for force with its abbreviation. Newton (N) 8. Bill, Jane and Peter are pulling on a rope with a force of 125N, 100N and 200 N, respectively. Fred, John and Lisa are pulling on the opposite end of the rope with a force of 150N, 130 N, and 150 N, respectively. What is the net force on the rope? Who wins the tug of war? Bill, Jane, Peter are pulling with a combined force of 425 N Net force = 430 N - 425 N Fred, John, Lisa are pulling with a combined force of 430 N Net force = 5 N Fred, John & Lisa win 9. List and briefly describe the 3 basic types of friction. Static friction: occurs when objects are in contact, but not moving Sliding friction: occurs when objects are in contact and sliding Rolling friction: occurs when objects are in contact and rolling (such as wheels) 10. How would you recognize if unbalanced forces are acting on an object? What would you observe? the object is accelerating 11. How would you recognize if balanced forces are acting on an object? What would you observe? object is either not moving or moving with constant velocity Free Body Diagrams 1. List the forces that are commonly used in drawing free body diagrams. Gravity, Normal, Friction, Applied, Air Resistance, Tension or Spring 2. Draw free body diagrams for the following: a. The 6 students in the tug of war contest in #8 on the previous page. b. A refrigerator being pushed up a ramp onto a truck. c. A skydiver falling through the air from a plane prior to opening his parachute.  d. The skydiver descending with his parachute open Gravity, Weight & Newton’s Law of Gravitation 1. To what kind of objects does Newton’s law of gravitation apply? All objects in the universe 2. What is weight? Weight is the gravitational force exerted on an object 3. What is the formula for weight? w = mg 4. How is it different from mass? mass is the amount of matter in an object, weight depends on mass and gravity 5. What is the value for Earth’s gravitational strength? (Don’t forget the units!) 9.8 m/s2 Newton’s Laws of Motion Newton’s 1st Law. 1. What does Newton’s 1st Law state? An object at rest or an object in motion will stay in that state unless acted upon by an unbalanced force 2. According to Newton, if the forces on an object are balanced, what does it say about the motion of the object? It will remain at rest until an unbalanced force acts on the object 3. What is inertia? The tendency of an object to resist change 4. Do all objects possess inertia? Yes 5. How does the mass of the object affect its inertia? Higher the mass, the greater the inertia 6. Do all objects resist changes in motion? Yes 7. Briefly explain how inertia works or is illustrated by passengers in a car. The car is traveling down the road at 50 mph, that means that the people in the car are moving at the same speed. If the car stops suddenly, the passengers will fly forward, until stopped by an outside force, like a seat belt. Newton’s 2nd Law. 1. What does his 2nd law state? The unbalanced force acting on an object is equal to the object's mass times its acceleration. 2. Does the 2nd law deal with balanced or unbalanced forces? Or both? unbalanced forces 3. What formula is used to describe his 2nd Law? F = ma 4. According to Newton’s 2nd Law, if I apply a force on an object what should it do? The mass doesn’t change, so the object would accelerate Newton’s 3rd Law 1. What does Newton’s 3rd Law state? For every action, there is an equal and opposite reaction 2. List 4 facts from the 3rd Law. 1. Forces act in pairs 2. Forces are the same size but in opposite directions 3. Forces do not act on the same object 4. Forces occur at the same time. Practice Problems: For each problem, write out the formula, substitute with the numbers and units, solve the problem, and give the answer with the correct units. v = d/t a=vf-vi/t p=mv p1 + p2 = p1 + p2 F=ma 1. What is the weight, in Newtons, of a 75 kg person? m = 75 kg w = mg w = 75 kg (9.8 m/s2) 2 g = 9.8 m/s w = 735 N 2. How much would the person weigh on the Moon if the gravitational attraction is 1.6 m/s2? m = 75 kg w = mg w = 75 kg (1.6 m/s2) 2 g =1.6 m/s w = 120 N 3. If a 150 kg person could stand on the surface of Jupiter the person would weigh 381 N. What is Jupiter’s gravitational strength? m = 150 kg w = mg 381 N = 150 kg (g) w =381 N g = 2.54 m/s2 4. What is the net force necessary for a 2000 kg automobile to accelerate forward at 5.0 m/s2? m = 2000 kg F = ma F = 2000 kg (5.0 m/s2) 2 a = 5.0 m/s F = 10,000 N 5. What is the acceleration of a 1500kg object if given a force of 500 N? m = 1500 kg F = ma 500 N = 1500 kg (a) F = 500 N a = 0.33 m/s2 6. In a test garage, a 2500 kg car goes from rest to 20 m/s in 5second. How much force would this car have on a wall if it crashed into it? m = 2500 kg a = (vf-vi)/t a= (20 m/s - 0)/ 5 s F = 2500 kg (4 m/s2) 2 v = 20 m/s F = ma a= 4 m/s F = 10,000 N t=5s F=? 7. A runner covers a distance of 50 meters in 4 seconds. If the runner has a mass of 55 kg, what is his momentum? m = 55 kg v = d/t v = 50 m/ 4s p = 55 kg (12.5 m/s) d = 50 m p =mv v = 12.5 m/s p = 687.5 kgm/s t=4s p=? 8. A toy truck has a momentum of 150 kg m/s. If the truck has a speed of 3.5 m/s, what is the mass of the truck? p = 150 kgm/s p = mv 150 kgm/s = m (3.5 m/s) v = 3.5 m/s m = 42.86 kg 9. The cue ball, with a momentum of 2 kg m/s, is hit into the stationary 8-ball. After the hit, the cue ball has a momentum of 1.25 kg m/s. What is the momentum of the 8-ball after the collision? 10. A cue ball, with a mass of 3 kg and a velocity of 5 m/s is crashed into a stationary baseball, with a mass of 4 kg. After the crash the cue ball is traveling at a velocity of 3 m/s. What is the velocity of the baseball?