Moving Energy Review

Two identical balls are rolling down a hill. Ball 2 is rolling faster than Ball 1.

Which ball has more kinetic energy (motion energy)?

• Ball 1 has more kinetic energy.

• Ball 2 has more kinetic energy.

• Both balls have the same amount of kinetic energy.

• More information is needed to determine which ball has more kinetic energy.

A student wearing roller skates is standing at the top of a hill. She wants to find out if she can get to the top of the other side just by coasting. She coasts down the hill and then up the other hill without pushing. The second hill is the same height as the first hill. As she coasts, her skates and the ground get a little warmer.

Will she have enough kinetic energy (motion energy) to coast to the top of the second hill? Why or why not?

• Yes, she will have enough kinetic energy to coast to the top of the second hill.

• Yes, she will have enough kinetic energy to coast to the top of the second hill because the second hill is the same height as the first hill.

• No, she will not have enough kinetic energy to coast to the top of the second hill. Some of her kinetic energy was destroyed.

• No, she will not have enough kinetic energy to coast to the top of the second hill. Some of her kinetic energy was turned into heat energy.

A cart full of apples is rolling along a road. As it rolls, many of the apples fall out of the cart. As the apples fall out, the total mass of the cart and apples decreases by half, but the speed of the cart does not change. What happens to the kinetic energy (motion energy) of the cart as the apples fall out?

• The kinetic energy of the cart decreases by half

• The kinetic energy of the cart is one fourth of what it was

• The kinetic energy of the cart doubles

• The kinetic energy of the cart stays the same

A 70 kg girl is riding her 3 kg skateboard along a level surface. She jumps as shown in the figure below, lands on the skateboard, and continues along at the same speed.

When the girl is in the air above her skateboard, does the girl or the skateboard have more kinetic energy (motion energy) and why?

• The skateboard has more kinetic energy than the girl because the girl gave the skateboard her energy.

• The girl has more kinetic energy than the skateboard because the girl is alive but the skateboard is not.

• The girl has more kinetic energy than the skateboard because the girl weighs more than the skateboard.

• The skateboard and the girl have the same amount of kinetic energy because they are traveling at the same speed.

Imagine a ball on a track where no energy is transferred between the ball and the track or between the ball and the air around it. The ball starts from rest at the position labeled Start and moves along the track toward the right.

What is the highest position the ball will reach before stopping and going back down the track? (Remember that no energy is transferred between the ball and the track or between the ball and the air around it.)

• Position 1 It depends on how much the ball weighs.

• Position 2

• Position 3

• It depends on how much the ball weighs.

Imagine a ball on a track where no energy is transferred between the ball and the track or between the ball and the air around the ball. The ball starts at Position 1 and goes down and up a dip on the track and past Position 2. Position 1 and Position 2 are at the same height.

Will the amount of energy the ball has at Position 2 be more, less, or the same as the total amount of energy the ball has at Position 1? Why? (Remember that no energy is transferred between the ball and the track or between the ball and the air around it.)

• The amount of energy the ball has will be more at Position 2 because new energy will be made when the ball goes down the steep side of the dip.

• The amount of energy the ball has will be less at Position 2 because energy will be used up when the ball goes up the long side of the dip.

• The amount of energy the ball has will be the same at Position 1 and Position 2 because the amount of energy in the system (ball and track) will not change.

• Whether the amount of energy of the ball is more, less, or the same at Position 2 compared to Position 1 depends on the speed of the ball before it gets to the dip.

Two students are running in a race. Student 1 has more kinetic energy (motion energy) than Student 2. Does Student 1 weigh more than, less than, or the same as Student 2?

• Student 1 weighs more than Student 2.

• Student 1 weighs less than Student 2.

• Student 1 weighs the same as Student 2.

• The only way to know which student weighs more is to also know how fast each student is running.

A person drops a rock off of a cliff. As the rock falls, its speed increases, and its mass stays the same. The person determined the speed of the rock at two time points. At Time 1, the rock was falling at 20 meters per second. At Time 2, the rock was falling at 40 meters per second.

How does the kinetic energy (motion energy) of the rock change from Time 1 to Time 2?

• The kinetic energy of the rock at Time 2 is zero.

• The kinetic energy of the rock has increased.

• The kinetic energy of the rock has stayed the same.

• The kinetic energy of the rock at Time 2 is the same as the kinetic energy at Time 1

In the morning, a student puts a warm can of soda in a cooler filled with ice.

He closes the cooler. A few hours later, the can of soda is colder. What happened to the total amount of energy in the cooler containing the can of soda and the ice? (Assume that no energy is transferred into or out of the cooler after it is closed.)

• The total amount of energy increased

• The total amount of energy decreased

• The total amount of energy stayed the same

• New energy was created so the total increased

Two girls are playing with two paper airplanes that are exactly the same. The girls stand the same distance from a wall and throw the airplanes toward the wall at different speeds. The first girl throws her airplane slower than the second girl. The nose of each airplane will be damaged when it hits the wall. Which paper airplane will be damaged the most when it hits the wall and why?

• The slower airplane will be damaged the most because it will take longer to hit the wall.

• The faster airplane will be damaged the most because it hits the wall with more speed.

• Both of the airplanes will be damaged the same amount because they are traveling the same distance.

• Both of the airplanes will be damaged the same amount because they are the same type of airplane.