Reference no: EM132787921

Question 1

a. Name one way in which the force of gravity and the electric force behave in the same way and one way in which they behave differently.

b. Electrons are tiny particles with very small negative charges. When two electrons are placed near each other, the electric force pushes them apart. What does this tell you about the mass of an electron? Explain.

Question 2

Marissa designs a robot that goes on a mission to Mars. The acceleration of gravity on Mars is less than half the acceleration of gravity on Earth.

a. How does the mass of the robot change once it gets to Mars? Explain.

b. How does the weight of the robot change once it gets to Mars? Explain.

Question 3

A motorcycle and its driver have a mass of 145 kg. Answer the following questions about it, using correct units.

a. The motorcycle has a kinetic energy of 47,000 J. What is the speed of the motorcycle?

b. The motorcycle climbs a ramp. How much gravitational potential energy has the motorcycle gained when it reaches a height of 3.5 m?

c. The motorcycle jumps off the ramp at a height of 4 m. What is the speed of the motorcycle at this point if its total mechanical energy is 62,500 J?

Question 4

A pear hangs in a tree at a height of 1.8 m. The pear has a mass of 0.12 kg. The pear falls out of the tree and lands on the ground. (Use correct units in all answers.)

a. Assuming no air resistance, how fast is the pear moving when it hits the ground?

b. Actually, air resistance converts 32.1% of the initial energy of the pear to heat energy by the time the pear lands. Based on this, how fast is the pear going when it hits the ground?

Question 5

Describe three energy transformations that are happening in the situation described below:

A tree grows in the sunlight. The tree is cut down and taken to a power plant, where it is burned. This heat is used to heat up steam, which turns a turbine to make electricity.

Question 6

You use a pulley system to lift a boat out of the water at a dock. When you use the pulley, the rope gets hot, and the pulley makes a loud whining sound. Give two reasons that the pulley system is less than 100% efficient.

Question 7

Brenda and Taylor push their car into the driveway because it will not start. The car has a mass of 850 kg. They apply a force of 800 N for 30 seconds to move the car 15 m. (Use correct units in all answers.)

a. What is their power?

b. Now they push the car all the way into the garage. They use a force of 600 N for 20 seconds, and use a power of 250 W. How far do they push the car?

Question 8

April does 1800 J of work to get a canoe moving from rest. April and the canoe have a mass of 70 kg.

a. What is her velocity after she does the work?

b. Later, she has the canoe going at a speed of 3 m/s. But friction between the canoe and the water does -200 J of work. How fast is the canoe going after this work is done?

Question 9

An incandescent lightbulb has a power of 100 W and is used for 4 hours. A microwave has a power of 1200 W and is used for 5 minutes.

a. Which device uses more electricity, and how much more?

b. How much energy would you save in 4 hours of use by switching from the incandescent lightbulb to a CFL lightbulb with a power of 23 W?

c. The CFL bulb has an efficiency of 9.9%, and the incandescent bulb has an efficiency of 2.2%. Which produces more light power, and by how much?