Physics science Assignment PDF

Physics Assignment:
Student Name:
Instructor Name:
Course Number:
16th April 2020

Multiple Choice
Highlight the correct answer in yellow. (2 points each)
1. A 1000-kg car is traveling at a speed of 10 m/s. If the speed of the car is increased to 20
m/s, the car’s kinetic energy is
A. doubled
B. halved
C. quadrupled
D. unchanged
Working
K.e = 1
2 m v2= 1
2 ( 1000 ) ¿
K.e = 1
2 m v2= 1
2 ( 1000 ) (20)2=200000
4(50000)=200000
2. The law of conservation of energy states:
A. mass is a form of energy
B. it is illegal to waste energy
C. the end product of all energy transformation is heat
D. energy transformations occur without a net gain or loss of energy
3. The SI unit for work is the
A. joule
B. watt
C. calorie
D. newton
4. The SI unit of energy is named after
A. Albert Einstein B. James Prescott Joule C. Count Rumford D. James Watt

5. The property something has that enables it to do work is
A. mass
B. force
C. momentum
D. energy
6.The wound spring of a watch possesses ___ energy
A. potential B. kinetic
C. chemical D. zero
7. A 75-kg window air conditioner falls a distance of 6 m to the street below (no one is injured).
What was the PE of the air conditioner while it sat at rest within the window frame?
A. 735 J
B. 2205 J
C. 3601.5 J
D. 4410 J
Working
PE=mgh=75×10 × 6=4500 J
8.In the cylinder of an automobile engine, the chemical energy of gasoline is initially
transformed into
A. mechanical energy B. heat energy
C. chemical energyD. potential energy
9. When the height of an object is changed, the gravitational potential energy ________
A. decreases
B. increases
C. depends on the reference point
D. remains constant
10.Which of the following objects has the greatest kinetic energy?
A. an object with a mass of 4m and a velocity of v
B. an object with a mass of 3m and a velocity of 2v
C. an object with a mass of m and a velocity of 4v
D. an object with a mass of 2m and a velocity of 3v
Working
Ke= 1
2 m v2= 1
2 ( 4 m ) v2 =2 mv2
Ke= 1
2 m v2= 1
2 ( 3 m ) (2 v)2 =6 m v2

Ke= 1
2 m v2= 1
2 ( m ) (4 v )2=8 m v2
Ke= 1
2 m v2= 1
2 ( 2 m ) ( 3 v)2 =9 m v2
Decide whether each statement is true or false.(2 points each)
___TRUE_______ 11. In a nuclear weapon, a small amount of matter is converted into energy.
____FALSE______ 12. Energy can be defined as the rate at which work is done.
____TRUE______ 13. Kinetic energy may be thought of as the energy of motion.
__TRUE________ 14.Farmer Ben attempts to remove an 80-kg rock from his field. If he
applies a force of 789 N for 10 seconds yet fails to move the rock, he has done no work.
____FALSE______ 15.Upon eating food, the chemical energy contained within the food is
destroyed by the process of digestion.
Fill in the Blank(2 points each)
16. Potential energy is often referred to as the energy of __position_ and kinetic energy as the
energy of _motion_
17. The SI unit for power is ___watt_____________
18. In the United states, the _industrial_sector consumes the most energy.
19. The total energy of a(n) _isolated _ system remains constant.
20. Renewable energy sources cannot be exhausted.
Matching(2 points each)
21. the energy an object has by virtue of it mass -Rest Energy.
22. measure of the tendency of a rotating object to continue spinning about a fixed axis- Angular
Momentum.
23. measure of the tendency of a moving object to
continue motion along a straight line- Linear Momentum
24. _ one newton-meter _ joule
25. _ the energy an object has by virtue of its position _ potential energy

YOU MUST SHOW YOUR WORK TO EARN FULL CREDIT(5 points each)
26. Distinguish between total energy and mechanical energy. When is total energy
conserved? When is mechanical energy conserved?
Total energy is the sum of all forms of energy present in an isolated system. On the other
hand, mechanical energy is the sum of kinetic energy and potential energy.
Total energy is conserved when the system is isolated (i.e. in a system that does not interact
with its surrounding) while mechanical energy is conserved when no work is done by
external forces (i.e. work is done only by internal forces)
27. A horizontal force of 80 N is used to move a 20-kg crate across a level floor. How much
work is done when the crate is moved 5 m? How much work would have been done if the
crate’s mass were 30 kg?
Work=Force × distance
Work=80× 5=400 Nm=400 J
Work done on the 30 kg mass=80 ×5=400 Nm=400 J
Work done=400 J
The same work would have been done since the same force would be used and the
load would have moved through the same distance.
It is worth noting that work done would only differ if the two masses were to be
lifted against the gravity (above the ground through the same distance)
28. How much work is needed to raise a 110-kg load of bricks 12 m above the ground to a
building under construction?
Work done is equivalent to the energy used. In this case work to be done would be
equivalent to the potential energy gained as the load is moved some distance above
the ground.
Work= potential energy=mgh Where m,g and h represent mass, gravitational pull
and height respectively.
Work= potential energy=mgh=¿110×10 ×12=13200 J
29. A total of 490 J of work is needed to lift a body of unknown mass through a height of 10
m. What is its mass?
Work done is equivalent to the energy used. In this case work to be done would be
equivalent to the potential energy gained as the load is moved some distance above the
ground.
Work= potential energy
Work= potential energy=mgh Where m,g and h represent mass, gravitational pull and
height respectively.

Work=mgh
490=m ×10 ×10
m= 490
10 ×10 =4.9
Mass=4.9 kg
30. How much power must the legs of a 50-kg woman develop in order to run up a staircase
5 m high in 7 s?
Power is the rate at which work is done.
The SI uint of power is the watt (W)
Power= work done
time = force ×distance
time = mgh
t where m,g,t and h represent mass, gravitational
pull, time and height respectively.
Power= mgh
t = 50 ×10 ×5
7
Power=357.14 W
Power to be developed by the legs is 357.14 W
31. An 80-kg mountaineer climbs a 3000-m mountain in 10 h. What is the average power
output during the climb?
Power is the rate at which work is done.
The SI uint of power is the watt (W)
Power= work done
time = force ×distance
time = mgh
t where m,g,t and h represent mass, gravitational
pull, time and height respectively.
Power= mgh
t = 80 ×10 ×3000
10 ×60 ×60
Power=66.67 W
Power output during the climb is 66.67W
32. A weightlifter raises a 90-kg barbell from the floor to a height of 2.2 m in 0.6 s. What
was his average power output during the lift?
Power is the rate at which work is done.
The SI uint of power is the watt (W)
Power= work done
time = force ×distance
time = mgh
t where m,g,t and h represent mass, gravitational
pull, time and height respectively.

Power= mgh
t = 90 ×10 ×2.2
0.6
Power=3300 W
Power output during lift is 3300W
33. A 1200-kg car is moving at a speed of 15 m/s. Find its kinetic energy.
Kinetic energy (k.e) is the energy possessed by a body by virtue of it being in motion.
The SI unit of kinetic energy is joule (J)
It is given by the formula
K . e=1
2 m v2
where m and v represent mass and velocity of the body respectively.
K . e=1
2 m v2=1
2 ×1200 ×152=135000 J
34. What is the speed of an 800-kg car whose kinetic energy is 250 kJ?
Kinetic energy (k.e) is the energy possessed by a body by virtue of it being in motion.
The SI unit of kinetic energy is joule (J)
It is given by the formula
K . e=1
2 m v2
where m and v represent mass and velocity of the body respectively.
250000= 1
2 mv2= 1
2 × 800 × v2
250000= 1
2 × 800 × v2
250000=400 v2
250000
400 =v2
√ 250000
400 =v
¿ 500
20 =v
25=v
Speed of the car is25 m/ s
35. A student who weighs 556 N climbs a stairway (vertical height of 4.0 m) in 25 s.
a. How much work is done?

Work done is equivalent to the energy used. In this case work to be done would be
equivalent to the potential energy gained as the student moves up the stairway
Work= potential energy
Work= potential energy=Wh Where W and h represent Weight of the student and height
moved respectively.
Work=Wh=556 × 4=2224 J
Work done is 2224J
b. What is the power output of the student?
Power is the rate at which work is done.
The SI uint of power is the watt (W)
Power= work done
time
Power=2224
25 =88.96 W
Power output of the student =88.96 W