Test Prep for AP® Courses

Given Table 7.7 about how much force does the rocket engine exert on the 3.0-kg payload?

1. 150 N
2. 300 N
3. 450 N
4. 600 N

Look at Figure 7.10(c). You compress a spring by x, and then release it. Next you compress the spring by 2x. How much more work did you do the second time than the first?

1. Half as much
2. The same
3. Twice as much
4. Four times as much

A crane is lifting construction materials from the ground to an elevation of 60 m. Over the first 10 m, the motor linearly increases the force it exerts from 0 to 10 kN. It exerts that constant force for the next 40 m, and then winds down to 0 N again over the last 10 m, as shown in the figure. What is the total work done on the construction materials?

1. 500 kJ
2. 600 kJ
3. 300 kJ
4. 18 MJ

A roller coaster is set up with a track in the form of a perfect cosine. Describe and graph what happens to the kinetic energy of a cart as it goes through the first full period of the track.

In what direction relative to the direction of travel can a force act on a car (traveling on level ground), and not change the kinetic energy? Can you give examples of such forces?

You are participating in the Iditarod, and your sled dogs are pulling you across a frozen lake with a force of 1200 N while a 300 N wind is blowing at you at 135 degrees from your direction of travel. What is the net force, and will your kinetic energy increase or decrease?

You are launching a 0.315-kg potato out of a potato cannon. The cannon is 1.5 m long and is aimed 30.0 degrees above the horizontal. It exerts an average 45 N force on the potato. Ignoring friction, what is the kinetic energy of the potato as it leaves the muzzle of the potato cannon?

Describe a system in which the main forces acting are parallel or antiparallel to the center of mass, and justify your answer.

A child has two red wagons, with the rear one tied to the front by a (non-stretching) rope. If the child pushes on the rear wagon, what happens to the kinetic energy of each of the wagons, and the two-wagon system?

A 1.0 kg baseball is flying at 10 m/s. How much kinetic energy does it have? Potential energy?

1. 10 J, 20 J
2. 50 J, 20 J
3. unknown, 50 J
4. 50 J, unknown

You have a 120-g yo-yo that you are swinging at 0.9 m/s. How much energy does it have? How high can it get above the lowest point of the swing without your doing any additional work, on Earth? How high could it get on the Moon, where gravity is 1/6 Earth’s?

A spring with a force constant of 5000 N/m and a rest length of 3.0 m is used in a catapult. When compressed to 1.0 m, it is used to launch a 50 kg rock. However, there is an error in the release mechanism, so the rock gets launched almost straight up. How high does it go, and how fast is it going when it hits the ground?

You are loading a toy dart gun, which has two settings, the more powerful with the spring compressed twice as far as the lower setting. If it takes 5.0 J of work to compress the dart gun to the lower setting, how much work does it take for the higher setting?

1. 20 J
2. 10 J
3. 2.5 J
4. 40 J

Old-fashioned pendulum clocks are powered by masses that need to be wound back to the top of the clock about once a week to counteract energy lost due to friction and to the chimes. One particular clock has three masses: 4.0 kg, 4.0 kg, and 6.0 kg. They can drop 1.3 meters. How much energy does the clock use in a week?

1. 51 J
2. 76 J
3. 127 J
4. 178 J

Old-fashioned pocket watches needed to be wound daily so they wouldn’t run down and lose time, due to the friction in the internal components. This required a large number of turns of the winding key, but not much force per turn, and it was possible to overwind and break the watch. How was the energy stored?

1. A small mass raised a long distance
2. A large mass raised a short distance
3. A weak spring deformed a long way
4. A strong spring deformed a short way

You are in a room in a basement with a smooth concrete floor (friction force equals 40 N) and a nice rug (friction force equals 55 N) that is 3 m by 4 m. However, you have to push a very heavy box from one corner of the rug to the opposite corner of the rug. Will you do more work against friction going around the floor or across the rug, and how much extra?

1. Across the rug is 275 J extra
2. Around the floor is 5 J extra
3. Across the rug is 5 J extra
4. Around the floor is 280 J extra

You do 30 J of work to load a toy dart gun. However, the dart is 10 cm long and feels a frictional force of 10 N while going through the dart gun’s barrel. What is the kinetic energy of the fired dart?

1. 30 J
2. 29 J
3. 28 J
4. 27 J

A child has two red wagons, with the rear one tied to the front by a stretchy rope (a spring). If the child pulls on the front wagon, the ____ increases.

1. kinetic energy of the wagons
2. potential energy stored in the spring
3. both A and B
4. not enough information

Which of the following are closed systems?

1. Earth
2. a car
3. a frictionless pendulum
4. a mass on a spring in a vacuum

A 5.0-kg rock falls off of a 10 m cliff. If air resistance exerts an average force of 10 N, what is the kinetic energy when the rock hits the ground?

1. 400 J
2. 12.6 m/s
3. 100 J
4. 500 J

Before railroads were invented, goods often traveled along canals, with mules pulling barges from the bank. If a mule is exerting a 1200 N force for 10 km, and the rope connecting the mule to the barge is at a 20 degree angle from the direction of travel, how much work did the mule do on the barge?

1. 12 MJ
2. 11 MJ
3. 4.1 MJ
4. 6 MJ