Laws of Motion
What does Newton’s First Law of Motion state about an object at rest?
A. It stays in motion forever.
B. It accelerates continuously.
C. It does not move because of friction.
D. It stays at rest unless acted upon by an unbalanced force.
D. It stays at rest unless acted upon by an unbalanced force.
In a uniform circular motion, what provides the force that keeps an object moving in a circle?
A. Centripetal force
B. Friction
C. Gravity
D. Inertia
A. Centripetal force
Which of the following correctly represents the formula for work done when the force and motion are in the same direction?
A. W = F x t
B. W = m x g
C. W = F x d
D. W = F x v
C. W = F x d
What does power measure?
A. The velocity of a moving object
B. The rate at which work is done
C. The total force exerted on an object
D. The amount of energy stored in an object
B. The rate at which work is done
What are the two main types of mechanical energy?
A. Heat energy and chemical energy
B. Nuclear energy and sound energy
C. Kinetic energy and potential energy
D. Gravitational energy and elastic energy
C. Kinetic energy and potential energy
Which of the following best represents Newton's Second Law of Motion?
A. F=ma
B. a = v/t
C. P = W/t
D. KE = (mv^2)/2
A. F=ma
What is the direction of an object’s velocity in uniform circular motion?
A. Tangent to the circular path
B. Along the radius of the circle
C. Toward the center of the circle
D. Opposite to the centripetal force
A. Tangent to the circular path
Which of the following must be true for work to be done?
A. No movement of the object is required.
B. The force must be applied continuously.
C. The force must be perpendicular to the motion of the object.
D. An object must move in the same direction as the force applied.
D. An object must move in the same direction as the force applied.
If 100 J of work is done in 2 seconds, what is the power output?
A. 20 W
B. 25 W
C. 50 W
D. 200 W
C. 50 W
Given: W=100J t=2s
Formula: P = W/t
Solution: P = 100J / 2s
Answer: 50 W
What is the formula for calculating kinetic energy?
A. KE = mv
B. KE = (mv^2)/2
C. KE = (mv)/2
D. KE = mv^2
B. KE = (mv^2)/2
If a person pushes a wall with 50 N of force, what force does the wall exert back on the person, and which law explains this?
The wall exerts 50 N of force in the opposite direction, explained by Newton's Third Law of Motion.
What is the formula for calculating centripetal force?
Fc = (mv^2)/t
ANSWER ONLY:
How much work is done if a 10.0 N force moves an object 3.00 m in the same direction?
Given: F=10.0N d=3.00m
Formula: W = F x d
Solution: W = 10.0N x 3.00m
Answer: 30.0 J
Why is a more powerful engine better suited for lifting heavier loads?
A more powerful engine can do the same amount of work in less time or perform more work in the same amount of time.
Why does a ball at the top of a hill have potential energy?
The ball has potential energy due to its position and the gravitational force acting on it.
ANSWER ONLY:
A 5 kg box is pushed with a force of 20 N on a frictionless surface. What is its acceleration?
Given: m=5kg F=20N
Formula: a=F/m
Solution: a=20N/5kg
Answer: 4 m/s^2
ANSWER ONLY:
A 2.0 kg object moves in a circle with a radius of 3.0 m at a speed of 4.0 m/s. Calculate the centripetal force acting on the object.
Given: m=2.0kg r=3.0m v=4.0m/s
Formula: Fc = (mv^2)/r
Solution: Fc=(2.0kg x (4.0m/s)^2) / 3.0m
Answer: 11 N
SOLVE ON THE BOARD:
A box with a mass of 10.0 kg is pushed across a level surface for a distance of 5.0 m. If 250 J of work is done, calculate the acceleration of the box.
Given: m=10.0kg d=5.0m W=250J
Formula: F = W/d a = F/m
Solution: F = 250J / 5.0 m = 50N
a = 50N / 10.0kg
Answer: 5.0 m/s^2
A 2,350 W motor is used to move an object with an acceleration of 12.5 meters per second squared for 15 seconds. If the object covers a distance of 50.0 meters, what is the mass of the object?
Given: P=2,350W d=50.0m t=15s a = 12.5m/s^2
Formula: W = P x t ; F = W/d ; m = F/a
Solution: W = 2,350W x 15 s = 35,250 J
F = 35,250J / 50.0m = 705 N
m = 705N / 12.5 m/s^2
Answer: 56 kg
SOLVE ON THE BOARD:
Calculate the kinetic energy of a 5.0 kg object moving at 3.0 m/s.
Given: m = 5.0kg v = 3.0m/s
Formula: KE = (mv^2)/2
Solution: KE = (5.0kg x (3.0m/s)^2)/2
Answer: 23 J
SOLVE ON THE BOARD:
A 10 kg object is initially at rest. A 50 N force acts on it for 5 seconds. What is its final velocity?
Given: m=10kg F=50N t=5s
Formula: a=F/m ; vf= vi + at
Solution: a=50N/10kg = 5m/s^2
vf = 0m/s + (5m/s^2)(5s)
Answer: 25 m/s
SOLVE ON THE BOARD:
A car is taking a curve with a radius of 50.0 m at a speed of 20.0 m/s. Calculate the required centripetal acceleration to keep it on the curve.
Given: r=50.0m v=20.0m/s
Formula: ac = (v^2) / r
Solution: ac = (20.0m/s)^2 / 50.0m
Answer: 8.00 m/s^2
A worker moves two identical boxes with a force of 50 N. In one case, the box is pushed horizontally for 4 m. In the other, the same box is lifted vertically to a height of 4 m. Compare the work done in both cases and explain any difference or similarity.
The work done is the same in both cases because the force applied and the distance moved are identical. However, the direction of the force relative to gravity differs, affecting the effort required.
A factory uses a motor that delivers 15,000 W of power to lift a 500.0 kg elevator vertically (assume the g= 9.8m/s^2). The elevator moves a distance of 40 meters in 10.0 seconds. Determine if the power of the motor is sufficient to lift the elevator at the given speed. If not, explain what needs to change (force, power, or speed) to make the motor capable of lifting the elevator.
Step 1: Calculate the work required to lift the elevator:
W = m x g x d
W = 500.0kg x 9.8m/s^2 x 40m
W=196,000J.
Step 2: Calculate the power required to lift the elevator in 10 seconds:
P=W/t
P = 196,000J / 10.0s
P = 19,600W.
Step 3: Compare the required power with the motor's power:
The motor delivers 15,000 W, but 19,600 W is required. Therefore, the motor is not sufficient to lift the elevator at the given speed.
Explanation:
To make the motor capable of lifting the elevator:
SOLVE ON THE BOARD:
Imagine you are in a physics lab, and you are working with a small object. You carefully lift a 7.3 kg object and place it on a shelf that is 3.25 meters above the ground. The object remains at rest on the shelf, and you want to determine how much energy it has stored due to its height.
Given that the acceleration due to gravity is g=9.8 m/s^2, how much gravitational potential energy does the object have?
Given: m = 7.3kg h = 3.25m g = 9.8m/s^2
Formula: GPE = m x g x h
Solution: GPE = 7.3kg x 9.8m/s^2 x 3.25m
Answer: 230 J