science 61 questions

An object weighing 75 N is dropped from the top of a building and falls a distance of 28 m to the ground. How much work does gravity do on the object from the time it is dropped to the time it hits the ground?

200 joules

How much work does a boy do by pushing on a parked car with 200N of force?

zero

___________________ measures the ratio of useful work output to work input.

Efficiency

A man pushes a crate along a factory floor by exerting a force of 55 N. If the crate moves a distance of 4.0 m, how much work does the man perform?

Energy is neither created nor destroyed.

The law of conservation of energy states that

Energy is neither created nor destroyed.

A feather will fall through the air more slowly than a brick because of ____.

air resistance

As you get farther from the center of Earth, your weight will ____.

it decreases

___________ is a quantity that measures how much a machine multiplies force or distance.

mechanical advantage

As Joan slides down the slide at the local park, all of the following energy changes occur EXCEPT

mechanical energy

. The relationship among mass, force, and acceleration is explained by ____.

they are directly proportinal

. If a marble with a mass of 0.03 kg, a baseball with mass of 0.4 kg, and a bowling ball with a mass of 6.3 kg are dropped at the same time from a height of 10 m above the surface of Earth, which will hit the ground first?

they will hit the ground at the same time

What are the units of power?

watts

Explain how the mass and weights are different from each other in Figure 4-1.

weight is the weight and mass is the space it takes up

Increasing the speed of an object ____ its potential energy.

will have no effect

___________ is a quantity that measures the effects of force acting over a distance.

work

Is it possible for a ball to have both kinetic energy and potential energy at the same time? Explain.

yes

You are a passenger in a vehicle which stops suddenly. According to Newton's first law, how will your body behave if you are NOT wearing a safety belt?

you will jerk forwards and then fall back again

. A 20-kg bicycle carrying a 50-kg girl is traveling at a speed of 8 m/s. What is the kinetic energy of the girl and bicycle?

1/2 (20 + 50) x 8 squared = 2290 Joules

A medicine ball has a mass of 5 kg and is thrown with a speed of 2 m/s. Find kinetic energy.

10 joules

A bowling ball rolls at a speed of 2.0 m/s and has kinetic energy of 12.0 J. What is the kinetic energy of the bowling ball when its speed is 1.0 m/s?

12 joules

An 18-kg bicycle carrying a 62-kg girl is traveling at a speed of 7 m/s. What is the kinetic energy of the girl and bicycle?

1519 watts

What is the gravitational potential energy of a 55 kg box that is 8.0 m above the ground?

4230 jouls

. The brakes on a car exert a frictional force of 6000 N in getting the car to stop. If the work done by the brakes is 120000 J in coming to a stop, how many meters did the car travel after the driver applied the brakes?

6000 m/s

. What is the height of a 2.5-kg mass that has gravitational potential energy of 196 J?

78.4 cm

An object has a kinetic energy of 810 J after falling a certain distance. If the mass of the object is 20 kg, what is the speed of the object at this time?

9 m/s

The acceleration due to gravity is ____.

9.8 m/s^2

. A 90-kg ceiling light is suspended 4 m above the floor. What is its gravitational potential energy?

90 kg x 4 m x 9.8 m/s squared= 3528 joules

Which of the following processes requires the most work?

A person lifting a 1kg weight 1m off the floor

A pendulum is swinging back and forth and has a kinetic energy of 400 J at a particular point in its path. Which of the following statements is false?

Both the kinetic and potential energy are decreasing.

Which ball in Figure 4-1 has the greatest potential energy?

D

You can calculate gravitational potential energy by using the equation ____.

GPE=MGH

The formula for calculating kinetic energy can be written as ____________________.

Ke= 0.5mv^2

You can calculate kinetic energy by using the equation ____.

Ke=0.5mv^2

A dump truck, a sports car, and a bicycle are traveling at the same velocity. Compare their kinetic energies

Kinetic energy is based on mass & velocity. If velocity is the same, the object with the most mass (the truck) will have the greatest kinetic energy, followed by the car. The bike would have the least kinetic energy

___________ is the stored energy resulting from the relative positions of objects in a system.

Potential Energy

According to Newton's second law of motion, ____.

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force

The kinetic energy of an object increases as its ____ increases.

Volocity

Which of the following statements about work and energy is false?

Work and energy are always equal.

Which of the following is an example of mechanical energy?

a moving car

For any object, the greater the force that's applied to it, the greater its ____ will be.

accelaration

___________ can be defined as the ability to do work.

energy

If you double the velocity of an object, you increase its kinetic energy by a factor of _______.

four

The upward force on an object falling through the air is ____.

frictional energy

. According to the law of conservation of energy, energy can change ____________________, but it cannot be created or destroyed.

from

A baseball is dropped from a height of 5 m. As the ball falls toward Earth, there is a decrease in

gravity

In the absence of air, a penny and a feather that are dropped from the same height at the same time will ____.

hit the ground at the same time

The SI unit for energy is the ____.

joules

What are the units of work?

joules

____________________is the energy of a moving object due to its motion.

kinetic energy

Gravitational potential energy depends on the

mass and height above the earths surface

The kinetic energy of an object depends on which of the following?

mass and speed

A weightlifter presses a 400 N weight 0.5 m over his head in 2 seconds. What is his power?

p=w/t p= 400n / 2s = 200 watts

Stored energy is called ____________________ energy.

potential

A baseball batter hits a pop fly. Which of the following energy changes is false as the ball flies up into the air?

potential energy

Explain the changes in energy when a child slides down a sliding board.

potential, kinetic, thermal and friction

___________ is a quantity that measures the rate at which work is done.

power

According to the law of conservation of energy, the total amount of energy in the universe ____.

remains constant

What is the difference between the energy provided by fats and the energy provided by carbohydrates and proteins?

the amount of energy produced

According to Newton's laws, what would happen if the force of Earth's gravity suddenly stopped pulling on the Moon?

the earths atmosphere would float into space

O / + Friction increases the amount of energy machines must use to do work.

true