Physics Ch. 8 & 9: Problem Set final Work, Energy & Law Of Conservation of Energy Mr. Marzouk

Name: ____________________________________ Blk: ________

1. Mikal has energy caused by his motion. This is

a) Kinetic energy b) thermal energy c) potential energy d) momentum

2. When you throw a ball up in the air, the total energy of the ball at any point in its

flight can be expressed as kinetic energy _________ potential energy.

a) Times b) minus c) plus d) divided by

3. If two bodies meet in an elastic collision, the total EK of the bodies before the

collision is _______ the total EK of the bodies after the collision.

a) Greater than b) equal to c) less than

4. Find the kinetic energy of an airplane traveling at a speed of 648 km/hr. The mass of the airplane

is 5000 kg.

5. Greg, who has a mass of 48 kg, climbs up a ladder to a diving platform 5.0 meters above the

ground. How much potential energy does he have?

6. Esther lifts a 90 kg barbell from a stand 0.90 meters off the ground to a height of 1.75 meters off

the ground. What is the increase in the potential energy of the barbell?

7. Rod, having a mass of 45 kg, is on a sled having a mass of 5.0 kg. If they together have a

kinetic energy of 260 J, how fast are they moving?

8. A basketball with a mass of 5 kg has the same kinetic energy as a bowling ball. The bowling ball

has a mass of 10 kg and is moving at a speed of 20 m/s. How fast is the basketball moving?

9. During a contest that involved throwing a 7 kg bowling ball straight up in the air,

Jennifer R. exerted a force of 810 N on the ball. If the force was exerted through a distance of

2.0 meters, how high did the ball go from the point of release?

10. In a fit of anger, Mr. Marzouk shot an unsuspecting physics student (who hadnt completed their

sample problems on time) with a paint gun (at long range). If the bullet, with mass of 5 grams,

fired forwards with a velocity of 15 m/s, with what velocity did the gun, mass of 3 kg, recoil?

Physics Ch. 8 & 9: Problem Set final Work, Energy & Law Of Conservation of Energy Mr. Marzouk

Name: ____________________________________ Blk: ________

Law of Conservation of Energy Problems 1. A student lifts his 2.0 kg pet rock 2.8 m straight up. He then lets it drop to the ground. Use the Law

of Conservation of Energy to calculate how fast the rock will be moving (a) half way down and (b)

just before it hits the ground.

2. A 65 kg girl is running with a speed of 2.5 m/s. How much kinetic energy does she have? She grabs

on to a rope that is hanging from the ceiling, and swings from the end of the rope. How high off the

ground will she swing?

3. How much kinetic energy will an 80.0 kg skier sliding down a frictionless slope (vertical height =

60.0 m) have when he 2/3 of the way down?

4. A golfer wishes to hit his drives further by increasing the kinetic energy of the golf club when it

strikes the ball. Which would have the greater effect on the energy transferred to the ball by the

driver --- doubling the mass of the club head or doubling the speed of the club head? Explain.

5. How much work must be done to increase the speed of a 14 kg bicycle ridden by a 68 kg rider from

9.4 m/s to 14.9 m/s?

6. A truck moving with a speed of 90 km/h loses it brakes but sees a runaway hill near the highway.

If the driver steers his vehicle into the runaway hill, how far up the hill (vertically) will the vehicle

travel before it comes to a stop? (Ignore friction.) If friction is taken into account, will the vertical

distance the vehicle moves be less or greater than the ideal distance you just solved for, neglecting

friction? Explain.

7. A rubber ball falls from a height of 2.0 m, bounces off the floor and goes back up to a height of 1.6

m. What percentage of its initial gravitational potential energy has been lost? Where does this

energy go? Has the Law of Conservation of Energy been violated?

Physics Ch. 8 & 9: Problem Set final Work, Energy & Law Of Conservation of Energy Mr. Marzouk

Name: ____________________________________ Blk: ________

8. A partially - filled bag of cement having a mass of 16.0 kg falls 40.0 m into a river from a bridge.

(a) What is the kinetic energy of the bag as it hits the water? (1 mark)

(b) Using energy considerations only, what vertical velocity does it have? (1 mark)

9. A block weighing 98.0 N falls 64.0 m.

(a) What is the potential energy of the block at 64.0 m? (1 mark)

(b) What is the kinetic energy of the block just as it strikes the ground? (1 mark)

(c) What speed does the block have as it strikes the ground? (1 mark)

10. During the hammer throw at a track meet an 8.0 kg hammer is accidentally thrown straight up. If

784.0 J of work were done on the hammer to give its vertical velocity, how high will it rise?

11. A 10.0 kg test rocket is fired from the center of the Pitt Meadows Secondary School track. Its fuel

gives it a kinetic energy of 1960 J before it leaves its launch pad. How high will the rocket rise?

12. A skater on a lake pushes on a 5.0 kg log to clear a skating area. If the skater does 600.0 J of work

on the log and the log is nearly frictionless, what is the velocity given to the log? (1 mark)

Physics Ch. 8 & 9: Problem Set final Work, Energy & Law Of Conservation of Energy Mr. Marzouk

Name: ____________________________________ Blk: ________

Work/Energy Review Notes

W = Fd Used where the magnitude of the force and displacement are considered

The F and d must be parallel to each other for any work to be done.

If F and d are in the same direction, the work is positive; if F and d are in

opposite directions, the work is negative... BUT this doesnt refer to

direction... WORK is a scalar or non-vector quantity (no direction).

The unit for work is a Joule, J = Nm = kgm2/s2.

WNET = W1 + W2 + ... If more than one force is doing work on an object, the total or net work

is the sum of the work done by all forces.

WNET = FNETd An alternative way to find the total or net work is to find the net force

first!

P = W/t Power is the rate at which work is done. It describes how much work a

machine can do in one second.

The unit for power is a Watt, W = J/s.

W = E The Work-Energy Principle: work done on an object will result in a

change in energy of that object.

The unit for energy is J, too.

Conversely, energy is the ability to do work.

Wgrav = EP Work against gravity results in gain in gravitational EP.

Work done by gravity results in a loss in gravitational EP.

EP = mgh EP depends only on 1) the mass of an object, and 2) its vertical height.

The higher the object, the more potential to fall

The amount of EP an object has in not physically important, the EP is!

Since EP depends on height, a point where EP = 0 must be chosen. It

should be chosen where the forces on the object are zero.

WNET = EK The net work done an object will change in its kinetic energy.

EK = 1/2mv

2 A change in EK means a change in velocity.

The Law of

Conservation of

Energy

The total mechanical energy of an object will always be constant

EK + EP = constant value... in other words, the total energy ETOT of an

object is always the same.

The total change in the mechanical energy of an object will always be

zero... EK + EP = 0... in other words, if you lose EP, you gain the same

amount of EK, and vice versa.