 A weightlifter lifts a barbell 0.65 m with a constant force of 435 N. If it takes 280 W to move the barbell, how many seconds did it take?

 Use the answer key handout to check and correct your homework.  DO NOT WRITE ON THE ANSWER KEY

Chapter 11

 Energy is the ability of an object to change itself, other objects, or the world around it.  Itself: Energy can be changed from one form to another  Other objects: Energy can be transferred from one object to another, often through collisions  Surroundings: Energy can be transferred (such as heat) to surroundings

 Kinetic  Potential ◦ Gravitational ◦ Elastic ◦ Electrical ◦ Chemical ◦ Mass

 The SI unit of energy is the Joule (J)  This is the same unit as work

 Kinetic energy is the energy an object has due to its motion

 Calculate the kinetic energy of a kg baseball traveling at 40.0 m/s

 Calculate the kinetic energy of a 1100 kg car backing up at 1.5 m/s.

 The work done to an object is equal to its change in kinetic energy

 A hockey player hits a 0.16 kg puck with a force of 120 N for a distance of 0.92 m. If before the slapshot the puck was moving forward at 1.4 m/s, what was the puck’s velocity after the shot?

 A soccer player is running towards a 0.43 kg soccer ball that is moving towards the goal at 0.76 m/s. When she reaches the ball, she kicks it with a force of 110 N for a distance of 0.43 m. What is the ball’s velocity after the kick?

 A collision is called elastic if kinetic energy is conserved  A collision is called inelastic if kinetic energy is not conserved  A collision is called perfectly inelastic if the two objects have the same final velocity (stuck together)  Momentum is always conserved in a closed, isolated system.

 Earth’s gravity pulls on a 13 kg rock as it falls from rest off of a cliff. Use the work-energy theorem to find the rock’s velocity after it has traveled 15 meters.

 Earth’s gravity pulls on a 50.0 kg rock as it falls from rest off of a cliff. Use the work- energy theorem to find the rock’s velocity after it has traveled 15.0 meters.

 Potential energy is energy that is stored in an object.  Many types of potential energy: ◦ Gravitational ◦ Elastic/spring ◦ Electrical ◦ Chemical ◦ Mass

 Gravitational potential energy is a result of the force of gravity between an object and another object (Earth).  m = object’s mass  g = acceleration due to gravity (9.8 m/s 2 )  h = height above a reference level (often the ground)

 Calculate the potential energy of a 18 kg child at the top of a 2.5 m tall slide.

 A 75 kg boulder is resting precariously at the edge of a cliff that is 32 m above the ground below. What is the potential energy of the rock?

 An airplane with mass of 3.7x10 5 kg is flying with a velocity of 89.0 m/s at an altitude of 3.1 km. What is the potential energy of the airplane?

 A 7.8x10 3 kg car is at the top of a hill. It drives down the hill where the elevation is lower by 23 m. If the top of the hill is the reference level, what is the car’s potential energy at the bottom of the hill?

 A 1.3 kg ball is thrown horizontally with a velocity of 4.2 m/s at a height of 1.9 m.  Calculate the ball’s kinetic energy  Calculate the ball’s gravitational potential energy

 Energy is conserved (just like momentum)  Since energy can be converted between its different forms, it is the sum of energy types that is conserved.  If no work (other than gravity) is done to a system:

 A kg baseball is thrown vertically from a height of 1.3 m with a velocity of 5.2 m/s. Assume air resistance is negligible. a) What is the maximum height of the baseball? b) What is the baseball’s velocity 2.4 m above the ground?

 Stanley (one of Mr. Szwast’s nephews) slides down a frictionless slide. The top of the slide is 2.4 m above the ground. The bottom of the slide is 0.3 m above the ground. If he pushes off to give him an initial velocity of 0.5 m/s, what is Stanley’s velocity at the bottom of the slide?

 A cannon shoots a 5.4 kg cannonball straight up at 95 m/s. This was a very bad decision, as the cannon was inside a building at the time. How fast is the cannonball traveling when it hits the ceiling 2.1 m above the cannon?

 A 1200 kg car is parked at the top of an icy hill. Its brakes fail, and it begins to slide down the hill. At the bottom of the hill, the car is traveling 7.1 m/s. What is the height of the hill?

 Top Thrill Dragster is one of the tallest, fastest roller coasters in the world. It shoots passengers out at 120 mph (53.6 m/s) up a track to a height of 420 ft (128 m). What is the velocity of the roller coaster at the top of the track? Ignore friction and air resistance.

VariableSymbolSI Unit of MeasurementSI Symbol Timetsecondss d m/s meters per second squared Force kg p (lower case) W Watts Kinetic Energy PE

 An astronaut hits a golf ball on the moon. The golf tee is m above the ground. The golf ball leaves the tee at 17.9 m/s. The ball hits the side of the lunar lander 4.43 m above the ground with a speed of 17.5 m/s. What is the acceleration due to gravity (g) at the surface of the moon?

 A raindrop falls from a rain cloud 1100 m above sea level. How fast is it moving just before it hits the ground if the elevation is 89m?  What is wrong with this problem?

 A 1250 kg rocket is launched with an initial velocity of 13 m/s. What is the maximum height that the rocket can reach?  What is wrong with this question?

 If your forces test score is still a D or F (below 140/200) you may retake it (again). You may do so Thursday or Friday after school next week.  Both worksheets are due Monday

 A 2.1 kg rock is thrown horizontally with a velocity of 7.2 m/s at a height of 1.8 m.  Calculate the ball’s kinetic energy  Calculate the ball’s gravitational potential energy

 No notes, no calculator, no purple sheet  When you are finished, turn it in at the front table and pick up both worksheets ◦ Momentum and Energy Review ◦ Momentum and Energy Crossword  No talking until ALL quizzes are submitted. If you appear to be talking (even if you have already turned in your quiz), you will receive a zero and have to retake the quiz.

 Potential Energy & Kinetic Energy – Wednesday  Conservation of Energy – Wednesday ◦ Typo on #3: v i = 5.10 m/s (not 2.10)  Momentum and Energy Review – Friday  Momentum and Energy Crossword – Friday

 An astronaut hits a golf ball on the moon. The golf tee is m above the ground. The golf ball leaves the tee at 17.9 m/s. The ball hits the side of the lunar lander 4.43 m above the ground with a speed of 17.5 m/s. What is the acceleration due to gravity (g) at the surface of the moon?

 Monday 10 th – Elastic and inelastic collisions  Tuesday 11 th – Review  Wednesday 12 th – Review  Thursday 13 th – Benchmark #2 (graphs)  Tuesday 18 th – Review worksheet  Wednesday 19 th (minimum day) – Review  Thursday 20 th (sub) – Test on momentum and energy  Week of 24 th – Review for and take final exam

 A collision is called elastic if kinetic energy is conserved  A collision is called inelastic if kinetic energy is not conserved  A collision is called perfectly inelastic if the two objects have the same final velocity (stuck together)  Momentum is always conserved in a closed, isolated system.

 A 2.00 kg black ball is rolling east at 3.00 m/s. A 5.00 kg gold ball is rolling west at 2.00 m/s. If the collision is elastic, what is the final velocity of each ball?

 This packet is due Thursday.  Mr. Szwast will answer questions before we take a quiz on the material.