Basic Forces
Newton's Laws
Friction
Drag
Work
Power
Kinetic and Potential Energy
Springs and more energy
100
One person pushes a box on a frictionless surface with a force of 1N in the negative x direction. This is the magnitude of the net force.
What is 1 N?
100
Newton's first law.
An object at rest will stay at rest unless acted upon by an outside force. An object in motion will stay in motion without changing direction or accelerating unless acted upon by an outside force.
100
READ THIS FIRST
(just view the answer)
Free points!
These coefficients of friction will be used for this problem set except for when specifically said otherwise.
100
Describe air resistance compared to weight, net force, and acceleration at terminal velocity
- Air resistance is equal to the objects weight
- No Net Force
- No Acceleration
100
What is the simpler equation (two forms) for work, and what do the components mean?
hat F * hat s
F s cos(theta)
The F stands for the force that is doing work, the s stands for the displacement. Theta is the angle between the two. It is a dot product.
100
What is the definition of power?
(Delta W)/(Delta t)
or
hat F * hat v
100
What is the work-energy theorem in condensed form? Different symbols are acceptable so long as they mean the same thing.
KEi + PEi + Wd = KEf + PEf
Initial kinetic energy plus initial potential energy plus work done equals final kinetic energy plus final potential energy.
100
What is the potential energy equation for a spring?
1/2 k x^2
100
Two people each exert a 1 N force on a box on a frictionless surface, both in the negative x direction. This is the magnitude of the net force on the box.
What is 2 N?
100
Newton's second law (the equation).
F = m a
100
How much force is required to first move a 20 kg wood crate on a wood floor?
50 N
100
What is 76 kg Caleb’s weight at terminal velocity?
760 N down
100
What is the more complex equation for work, and what do its symbols mean?
W = int_(x_1)^(x_2) F(x) dx
W is work, x1 and x2 are the starting and ending positions, and F(x) is the force being applied.
100
A car does 2450-J of work in 8 seconds. What is the power of the car?
306 W
100
How much gravitational potential energy do you have when you lift a 15 N object 10 meters off the ground?
150 J
100
What is the full, expanded work-energy theorem? Use the equations, not symbols.
mgh_i + 1/2 m(v_i)^2 + 1/2 k(x_i)^2 + W_d = mgh_f + 1/2 m(v_f)^2 + 1/2 k(x_f)^2
Initial gravitational potential energy plus initial kinetic energy plus initial spring potential energy plus work done equals final gravitational potential energy plus final kinetic energy plus final spring potential energy.
100
Two people each exert a 1 N force on a box on a frictionless surface. One pushes in the negative x direction, while the other pushes in the positive y direction. This is the magnitude of the net force on the box.
What is 1.41 N?
100
Newton's third law.
For every action, there is an equal and opposite reaction.
100
How much force is required to keep a 20 kg wood crate moving at a constant velocity on a wood floor?
40 N
100
What is the air resistance on 76 kg Caleb at terminal velocity?
760 N up
100
How much work is done when a force of 50 N is applied to move a box 6 meters?
300 J
100
Joe the physics teacher can go up a flight of stairs in 15 seconds. If the physics teacher weighs 850 N and the vertical height of the stairs is 10 m, what is Joe’s power output?
567 W
100
How much kinetic energy does a 0.15 kg ball thrown at 24 m/s have?
43.2 J
100
An intrepid physics student decides to try bungee jumping. She obtains a cord that is 12 m long and has a spring constant of 300 N/m. When fully suited, she has a mass of 69 kg. She looks for a bridge to which she can tie the cord and step off. Determine the minimum height of the bridge L, that will allow her to stay dry (that is, so that she stops just before hitting the water below). Assume air resistance that is negligible.
21.95 m
100
Three people each exert a 1 N force on a box on a frictionless surface. One pushes in the negative x direction, one pushes in the positive y direction, and one pushes in the direction 30 degrees below the positive x axis. This is the magnitude and direction of the net force on the box.
What is 0.518 N at an angle of 15 degrees from the positive y axis to the negative x axis?
100
How much force is required to accelerate a 795 kg Lorinser Speedy by 15 m/s2?
F = 11925 N
100
A 7.5 kg box of unknown material is resting on a concrete floor. It requires 63 N of force to first start the box moving and 45 N of force to keep it moving at a constant velocity. What is the coefficient of static friction of the unknown material and the concrete floor?
μ=0.84
100
When does linear drag apply?
Small objects in thick fluids.
100
A student lifts a physics book applying a force equal to is 10 N weight a distance of 3 m up. How much work did the student do on the book?
30 J
100
How much force is required to move an object 25 meters in 6 seconds with a power output of 50 watts?
12 N
100
If you throw a 0.15 kg ball straight down with 10 m/s of speed, how high off the ground must it be to have 100 J of total energy?
63 m
100
A mass of 0.80 kg is given an initial velocity vi = 1.2 m/s to the right, and then collides with a spring of force constant k = 50 N/m. Calculate the maximum compression of the spring.
0.1518 m
100
This is the net force.
What is 40 N left?
100
What is the mass of an object if it takes a net force of 40 N to accelerate at a rate of 0.88 m/s2?
m = 45.45 kg
100
A 7.5 kg box of unknown material is resting on a concrete floor. It requires 63 N of force to first start the box moving and 45 N of force to keep it moving at a constant velocity. What is the coefficient of kinetic friction of the unknown material and the concrete floor?
μ=0.6
100
The quadratic drag equation is as follows:
What do all the symbols mean?
is the drag force
is the density of the fluid
is the velocity of the object,
is the reference area (area at largest cross-section)
is the drag coefficient – a dimensionless coefficient related to the object's geometry
100
Sergio pushed a box with 50 N of force forward. When it did not move he pushed the box even harder with 100 N of force but the box still did not move. When did Sergio do more work?
Neither. The box didn't move in either case, meaning he did no work.
100
What is the power output of a person that pushes the box 5 meters in 3 seconds with a constant force of 12 N?
20 W
100
A 1.5kg rock has 50 J of potential energy when dropped. What is its kinetic energy when it hits the ground?
50 J
100
A ball in a pinball machine has a mass of 0.015 kg. Before launching, the spring it sits on is compressed 0.3m. The spring has a spring constant of 120 N/m. If the spring is released pointing straight up, what is the max height the ball will reach? Assume that zero is at the height of the relaxed spring.
36.73 m
100
A constant forward net force of 1000 N is applied to car with a total mass of 1500 kg. This is how much faster it will be travelling after 4 seconds.
What is 2.67 m/s?
100
How much force is required to accelerate a 0.142 kg baseball to 44.7 m/s during a pitchers 1.5 meter delivery?
F = 94.58 N
100
A 250 N rubber block on a concrete surface and is moving with 300 N of force is applied horizontally. The coefficient of kinetic friction is 0.8. What would the final velocity of the rubber block be if this 300 N force were applied from rest for 1.5 seconds?
vf = 6 m/s
100
Determine the drag coefficient of a 75 kg skydiver with a projected area of 0.33 m2 and a terminal velocity of 60 m/s.
Cd = 1.22
100
A sled is pulled by a boy with a force of 60 N at 35° from the horizontal. How much work is done if the sled moved 15 m forward?
735 J
100
What is your power output when applying 12 N of force on an object at an angle of 25° above the horizon to move it 5 meters horizontally in 3 seconds?
18.2 W
100
A 1.5kg rock falling at 6 m/s is 35 m off the ground. What is its velocity when it hits the ground?
27.13 m/s
100
A ball in a pinball machine has a mass of 0.015 kg. Before launching, the spring it sits on is compressed 0.3m. The spring has a spring constant of 120 N/m. If the spring is released pointing straight up, what is the max velocity the ball will reach?
26.8 m/s.
100
This is the magnitude of the force required to stop a 1000 kg car moving at a speed of 30 m/s within 5 seconds.
What is 6000 N?
100
A 0.050 kg golf ball leaves the tee at a speed of 75.0 m/s. The club is in contact with the ball for 0.020 s. What is the net force of the club on the ball?
F = 187.5 N
100
A 10 kg box is pulled with 170 N of force at an angle of 30° above the horizontal. The coefficient of kinetic friction between the floor and the box is 0.25. What is the acceleration of the box?
a = 14.35 m/s2
100
Estimate the terminal speed of a wooden sphere (wood density 0.830 kg/m3 ) falling through air if its radius is 8.00 m and its drag coefficient is 0.500. The density of air is 1.2 kg/m3. The volume of a sphere is (4/3)pi(r3).
17.00 m/s.
100
How much work do you have when 12 N of force were applied on an object at an angle of 25° above the horizon to move an object 5 meters horizontally?
54.5 J
100
A woman is pulling her luggage with a 25 N force at an angle of 55°. What is her power output if it takes her 15 seconds to pull the suitcase 20 m forward?
19.07 W
100
How much potential energy does a 1.5kg rock have when dropped if it is going 26 m/s when 5 meters from the ground?
582 J
100
A ball in a pinball machine has a mass of 0.015 kg. Before launching, the spring it sits on is compressed 0.3m. The spring has a spring constant of 120 N/m. In this case, the launcher is in a pinball machine, at an angle of 25 degrees from the horizontal. How far up the infinitely-long pinball table will the ball travel?
86.91 m
100
This is how fast a 10 kg box is going to be moving from rest after 3 seconds if a 200 N force is applied to the left and a 50 N force is applied to the right.
What is 45 m/s?
100
Joe and his sailboat have a combined weight of 450 kg. How far has Joe sailed when he started at 5 m/s and a gust of wind provided 600 Newtons of force for 4 seconds?
x = 30.64 m
100
The block on the front of the cart is 4 kg. The coefficient of static friction between the cart and the block is 0.7. How fast must the cart be accelerating to keep the block in place?
14 m/s.
100
A sports car has a coefficient of drag of 0.3 and a max cross-sectional area of 4 meters squared. If it can put out 12,000 N of force, what is its max velocity?
129 m/s.
100
A 12kg box is being pushed along a rough surface at a constant speed. The coefficient of friction between it and the surface is 0.8. If it moves 20m, how much work has been done by the pushing force? By friction? By gravity?
The pushing force does 1882 J of work.
The friction force does -1882 J of work.
Gravity does not do work.
100
You’re riding a toboggan down an icy run to a frozen lake, and you accelerate the 80.0-kg combination of you and the toboggan from 1.0 m/s to 2.0 m/s in 2.0 s. How much power does that require?
60 W
100
An roller coaster cart is traveling 4 m/s at the top of a hill 61 meters off the ground. How fast is it traveling at top of a second hill 24 meters off the ground?
27.49 m/s
100
A spring is compressed a distance X=2m and has a spring constant of 200 N/m. A box with a mass of 20 kg is resting against it. For the distance in which the spring is touching the box, there is no friction. Once the box is off the spring, the friction coefficient is 0.6. How far will the box go?
3.40 m
100
Sara pulls a 45 kilogram wagon with a force of 200 Newtons at a 25° angle to the horizontal from rest. This is how fast the wagon will be moving after 3 seconds.
What is 12.09 m/s?
100
The system is remaining at rest. There is no friction. What is the mass of the block on the ramp?
34.9 kg
100
M1=70 kg. M2=65 kg. The top block is 100m from the edge of the roof. The coefficient of kinetic friction between the top block and the roof is 0.6. If the initial velocity of the system is 30 m/s, will the top block fall?
Yes
100
The drag constant of a skydiver is 2.1. They have a mass of 50 kg. What is their terminal velocity?
Hint: drag constant is made of drag coefficient, fluid density, and cross-sectional area.
21 m/s.
100
A table of mass 40 kg is accelerated from rest at a constant rate of 2m/s2 for 4s by a constant force. What is the net work done on the table?
128 J
100
A motorized winch is rated at 10.0 kW. At what maximum constant velocity can this winch raise a mass of 27,500 kg?
0.037 m/s
100
You drop a box down the side of a completely vertical cliff. The box has a mass of 40 kg and a coefficient of friction of 1.2 with the cliff face. The cliff is 40m in height. Find the box's velocity at the bottom of the cliff and the amount of work friction does.
The box will be moving at 28 m/s. Friction does no work.
(hint if you're confused: friction is normal force times coefficient. Does the cliff exert any normal force on the box?)
100
A spring is compressed a distance X=2m and has a spring constant of 200 N/m. A box with a mass of 20 kg is resting against it. For the distance in which the spring is touching the box, there is no friction. Once the box is off the spring, the friction coefficient is 0.6. If the compression of the spring is doubled, how far will the box go?
13.61 m
100
A rocket has a mass of 12,000 kg, which we will assume remains constant for this problem. If the rocket applies a 200,000 N force on itself, pointing straight up, this is how far it will have travelled after 30 seconds. Assume the rocket is just taking off from Earth's surface. Round to the nearest meter.
What is 3091 m?
100
Tom pulls a 45 kilogram wagon with a force of 200 Newtons at a 15° angle to the horizontal from rest. How much faster will the wagon be moving after 2 seconds?
vf = 8.58 m/s
100
The block on the front of the cart is 4 kg. The coefficient of static friction between the cart and the block is 0.7. How fast can the cart be accelerating before the block slips?
16.4 m/s.
100
The drag coefficient of a parachute is 1.75. If a parachute is circular with a radius of 4m, what is the largest person it can safely slow to 8 m/s?
345 kg
100
The ski slopes at Bluebird Mountain make use of tow ropes to transport snowboarders and skiers to the summit of the hill. One of the tow ropes is powered by a 22-kW motor which pulls skiers along an icy incline of 14° at a constant speed. Suppose that 18 skiers with an average mass of 48 kg hold onto the rope and suppose that the motor operates at full power. Determine the speed at which the skiers will ascend the hill.
11 m/s
100
A 940 W motor is used to lift 200 kg of supplies 11 m above street level to the roof of a building. If the motor ran for 24s how much work did it do?
22,560 J (the mass and distance are unnecessary)
100
A box is at the top of a ramp sliding down, starting from rest. The ramp and the box have a coefficient of kinetic friction of 0.4. The ramp is 40m long (along the ground) and 20m tall. The box is 15 kg. How fast is the box moving at the bottom?
8.86 m/s
100
A spring is compressed a distance X and has a spring constant of 200 N/m. A box with a mass of 20 kg is resting against it. For the distance in which the spring is touching the box, there is no friction. Once the box is off the spring, the friction coefficient is 0.6. How much does the spring have to be compressed for the box to go 40m?
6.86 m