physics exam 1

A Honda Civic Hybrid weighs about 3100 lb . Calculate the mass of the car in kilograms. (Note: 1 kg on Earth's surface has a weight of 10 N).

m = 1400 kg

_______ friction acts on a sliding heavy table than on a lighter one.

more

Answer the following question by entering the numeric value with appropriate units. If the length of one side of a square is 12.0 m, what is the perimeter of the square?

perimeter = 48.0 m

According to Galileo, inertia is a

property of all matter.

The force that directly propels a motor scooter along a highway is that provided by the _______. View Available Hint(s)

road

First Law Law of Inertia

Every object continues in a state of rest or of uniform speed in a straight line unless acted on by a nonzero force.

Find the strength of the net force produced by a 20-N force and a 12-N force in each of these cases. The two forces act in opposite directions.

F = 8.0 N

Henry Heavyweight weighs 1100 N and stands on a pair of bathroom scales so that one scale reads twice as much as the other. What is the second scale readings?

W2 = 370 N

A car traveling with constant speed travels 150 km in 7200 s. What is the speed of the car?

2.1×10^−2 km/s

Both ends of a piece of rope are pulled by two people in a tug-of-war. If each pulls with a 400-N force, the tension in the rope

400 N.

Kinetic Energy

Energy in motion.

Power

Power is the measure of how fast work is done; it is the rate of work.

Equilibrium:

Sum of all forces equal zero

Aristotle:

Used common observations, not experiments Force is needed to keep an object in motion

Volume

he amount of space an object occupies

Density

mass per unit of volume, D = M/V

work

using a force to displace something

A ball is thrown straight up with enough speed so that it is in the air for several seconds. Assume the positive direction is upwards What is its velocity 0.70 s after it reaches its highest point?

v = -7.0 m/s

The gain in speed each second for a freely falling object is about

10 m/s.

How would air resistance affect the travel time?

Air resistance would increase travel time.

How would greater air resistance affect the travel time?

Air resistance would increase travel time.

Impulse

The change in momentum

A Honda Civic Hybrid weighs about 3100 lb . Calculate the weight of the car in newtons. (Note: 0.22 lb =1N).

W = 1.4×104 N

The sketch shows a painter's scaffold in mechanical equilibrium. The person in the middle weighs 480 N , and the tension in each rope is 320 N . What is the weight of the scaffold?

W = 160 N

If your mass is 84 kg , find your acceleration.

a = 0.60 m/s^2

In contrast to Aristotle's way of explaining nature, Galileo relied on

experiment.

When numbers are very small or very large, it is convenient to either express the value in scientific notation and/or by using a prefix with the unit. A pain-relieving pill has a mass of 0.005 g. Express the pill's mass in grams using scientific notation or in milligrams.

mass = 5×10^−3 g

Acceleration

net force / mass

Energy

property of a system that allows it to do work

When the strong man shown (Figure 1) exerts a downward force of 820 N on the rope, how much upward force is exerted on the block?

820 N

Weight:

Amount of gravitational pull on an object

Scales

Downward force -Gravity Support (upward) force -Scale reading

How does the time of ascent compare with the time of descent?

The time of ascent equals the time of descent.

Air Resistance

a type of friction that opposes motion.

Action and reaction pairs of forces always act on

different bodies

A ball is thrown straight up with an initial speed of 28 m/s . Find a height that the ball will reach m (neglecting air resistance).

h = 39 m

When an object is in dynamic equilibrium, it _______.

is moving in a straight line at a constant speed

Suppose a monkey weighs 107 N and the vine supporting her pulls upward with a force of 150 N. If the vine that supports the monkey breaks, what is then the net force on the monkey?

107 N

Torque can be calculated by multiplying the force (N) applied at 90∘ to the lever arm at a distance (m) from the pivot point (point of rotation), the compound SI unit for the torque is N⋅m. If the force (at 90∘ to the lever arm) applied is 15 N and it is applied at 2.0 m from the pivot point (point of rotation), what is the torque on the lever?

30 N⋅m

Would acceleration be greater or less if the ramp were a bit less steep?

Acceleration would be less on a less-steep ramp

Static:

Anything not moving and balanced Velocity and acceleration are 0

A ball is thrown straight up with an initial speed of 28 m/s . How much time does it take for the ball to reach the top of its trajectory?

t = 2.8 s

A horizontal force of 170 N is required to push a bookcase across a floor at a constant velocity. How much is the friction force that acts on the sliding bookcase?

Ffr = -170 N

Momentum

Inertia in motion

Simple Machines

Machines multiply forces

Inertia

inertia is not a force; it is a property of all matter to resist changes in motion. The quantitative measure of inertia is the mass of the object.

Part complete A baseball weighs 1.5 N on Earth. Another type of ball weighs 1.5 N on the Moon. The ball with the greater mass is the other type of ball. same for each. baseball. not enough information

other type of ball.

Suppose a monkey weighs 105 N and the vine supporting her pulls upward with a force of 130 N. Describe her motion.

The monkey accelerates upward while the force acts.

Mass:

The quantity of matter in an object A measure of inertia or sluggishness that an object has in response to an effort to start it, stop it, or change its state of motion

Net Force

The sum of all forces acting on an object

Earth pulls on the Moon. Similarly the Moon pulls on Earth, evidence that -Earth's and Moon's pulls comprise an action-reaction pair. -Earth and Moon pull on each other. -both of the above -none of the above

both of the above

Knowing that a 1.2-kg object weighs 12 N , find the acceleration of a 1.2-kg stone in free fall .

a = 10.0 m/s^2

Elastic collisions

stay separate before and after the collision

Ten seconds after starting from rest, a freely-falling baseball will have a speed of about

100 m/s.

When a baseball player hits a ball with a force of 1000 N, the ball exerts a force on the bat of

1000 N.

In the textbook we learn that the cause of acceleration is given by Newton's second law: a=Fnet/m. Find the acceleration that can result from a net force of 17 N exerted on a 2.8-kg cart. (Note: The unit N/kg is equivalent to m/s2.).

6.1 m/s^2

Leslie's average speed when she runs to the store 13 km away in 28 min is V avg = 28 km/h How fast is this in m/s?

7.7 m/s

By how much does its speed increase each second while it is descending?

9.8 m⋅s^−1

In the absence of air resistance, a ballplayer tosses a ball straight up. By how much does the speed of the ball decrease each second while it is ascending?

9.8 m⋅s^−1

Would acceleration be greater or less if the ramp were a bit less steep?

Acceleration would be less on a less-steep ramp.

According to Aristotle, how fast do heavy objects fall compared to light objects?

Aristotle stated that heavy objects fall faster than light objects.

In cases A, B, and C, the crate is in equilibrium (no acceleration). From greatest to least, rank the amount of friction between the crate and the floor. Assume that F1 = 100 N , F2 = 120 N , and F3 = 130 N .

C B A

A horizontal force of 170 N is required to push a bookcase across a floor at a constant velocity. How much friction acts on the bookcase when it is at rest on a horizontal surface without being pushed?

Ffr = 0 N

Driving along the road at 98 km/h , Reckless Rick runs into Hapless Harry, who is directly in front of him and is driving at 62 km/h . What is the impact speed—that is, the speed of the two vehicles the moment after collision?

v = 36 km/h

Three parachutists, A (75 kg ), B(50 kg ), and C(40 kg ), each have reached terminal velocity at the same altitude. From fastest to slowest, rank their terminal velocities.

A B C

Three parachutists, A (75 kg ), B(50 kg ), and C(40 kg ), each have reached terminal velocity at the same altitude From longest to shortest times, rank their order in reaching the ground.

C B A

Find the average speed of a tennis ball when it travels the full length of the court, 24 m, in 0.60 s .

V avg = 40 ms

Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 340 N . What is Lucy's weight?

W = 680 N

Find the acceleration for a ball that starts from rest, rolls down a ramp, and gains a speed of 30 m/s in 3.6 s

a = 8.3 m/s^2

A horizontal force of 170 N is required to push a bookcase across a floor at a constant velocity. Part complete What is the net force acting on the bookcase?

F = 0 N

Lillian rides her bicycle along a straight road at average velocity v. If Lillian's average speed is 7.9 m/s for a time of 4.0 min , find the distance that she travels.

d = 1900 m

Lillian rides her bicycle along a straight road at average velocity v. Write an equation showing the distance she travels in time t.

d = vt

Compared with a 1-kg block of solid iron, a 2-kg block of solid iron has the same mass. weight. volume. all of the above none of the above

none of the above

A school bus slows to a stop with an average acceleration of -2.3 m/s2 . Find the time that the bus takes to slow from 11.0 m/s to a stop.

t = 4.8 s

Friction

The resistance that one surface or object experiences when moving over another

A business jet of mass 34000 kg takes off when the thrust for each of two engines is 40000 N. Find its acceleration.

a = 2.4 m/s^2

Vacuum

a space with all of the air molecules removed and pressure is so low, so that air resistance does not affect any processes being carried out inside (remember...there is no such thing as a "perfect" vacuum).

In a vacuum,

a stone and a feather will fall at the same rate if dropped from the same height and at the same time.

inelastic collisions

coupled after the collision

Suppose a monkey weighs 105 N and the vine supporting her pulls upward with a force of 130 N. What is the net force on the monkey?

25 N

Second Law Law of Acceleration

An object accelerates in the direction of the unbalanced force.

Potential Energy

An object is at its maximum potential energy when it is at it's maximum height (v=0).

Dynamic:

An object that moves at constant velocity is in equilibrium When the sum of all forces equal0on a moving object, it is in equilibrium

Conservation of Energy

Energy cannot be created or destroyed; it may be transferred from one form into another, but the total amount of energy never changes.

A simple rearrangement of Newton's second law gives Fnet=ma. Find a net force that is needed to give a 7.0-kg package an acceleration of 6.8 m/s2 . (Note: The units kg⋅m/s2 and N are equivalent.).

Fnet = 48 N

Third Law Law of Action -Reaction

For every action, there is an equal and opposite reaction.

Weight depends on:

Mass: The greater the mass, the greater the weight* Gravity: The greater the gravity, the greater the weight

Calculate your average walking speed when you step 1.4 m in 0.56 s .

Vavg = 2.5 m/s

A different scaffold that weighs 420 N supports two painters, one 500 N and the other 420 N . The reading in the left scale is 740 N . Part complete What is the reading in the right-hand scale?

W = 600 N

A ball is thrown straight up with enough speed so that it is in the air for several seconds. Assume the positive direction is upwards. What is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity?

a = -10 m/s^2

In the textbook acceleration is defined as a=Δv/Δt. Use this formula to find the acceleration of a cart on an inclined plane that gains 5.0 m/s each 1.7 s .

a = 2.9 m/s^2

A ball is thrown straight up with enough speed so that it is in the air for several seconds. Assume the positive direction is upwards. What is the change in velocity, v, during this 0.70-s interval?

Δv = -7.0 m/s

A force F acts in the forward direction on a cart of mass m. A friction force f opposes this motion. use Newton's second law and express the acceleration of the cart.

a = F−f/m

A glance at the speedometer on your vehicle will tell you your

instantaneous speed.

Find the net force produced by a 32-N force and a 25-N force in each of these cases. Both forces act in the same direction.

F = 57 N

Suzie Skydiver with her parachute has a mass of 55 kg. Before opening her chute, what force of air resistance will she encounter when she reaches terminal velocity?

F = 550 N

Suzie Skydiver with her parachute has a mass of 55 kg. What force of air resistance will she encounter when she reaches a lower terminal velocity after the chute is open?

F = 550 N

When two horizontal forces are exerted on the car, 250 N forward and 180 N backward, the car undergoes acceleration. What additional force is needed to produce non-accelerated motion?

F = 70 N backward

A firefighter of mass 80 kg slides down a vertical pole with an acceleration of 4.2 m/s2. friction force that acts on the firefighter.

Ffr = 450 N

Marie is pushing horizontally on a table that slides across the floor at constant velocity. If she pushed with the same amount of force, but directed that force downward a bit, how would the amount of friction of the table legs with the floor be affected?

Friction would increase.

A friend says that Ale´ cannot push on the tree unless the tree pushes back on her, and another friend says that if Ale´ pushes quickly, the tree won't push as hard on her. Which friend do you agree with, and why?

The first friend. Whatever push she exerts on the tree, briefly or otherwise, the pushback by the tree will be equal and opposite. That's Newton's 3rd law.

Galileo:

Used experimentation and data No force needed to keep an object in motion Motion occurs with respect to inertia

Find the average speed of a tennis ball when it travels the full length of the court, 24 m, in 0.52 s .

V avg = 46 m/s

Find the average speed of a rabbit that runs a distance of 24 m in a time of 1.8 s .

V avg = 13 m/s

Find Leslie's average speed when she runs to the store 13 km away in 28 min .

V avg = 28 km/h

Henry Heavyweight weighs 1100 N and stands on a pair of bathroom scales so that one scale reads twice as much as the other. What is the first scale readings?

W1 = 730 N

Find the acceleration for a ball that starts from rest and rolls down a ramp and gains a speed of 26 m/s in 5.0 s .

a = 5.2 m/s^2

An astronaut of mass 120 kg recedes from her spacecraft by activating a small propulsion unit attached to her back. The force generated by a spurt is 28 N. Find her acceleration.

a = 0.23 m/s^2

Find a distance that a freely falling rock drops when it falls from rest for 4.0 s .

d = 80 m

The acceleration of a hamster is 4 m/s2 when it increases its velocity from rest to 12 m/s in 3 s. Select the option that shows that the hamster travels a distance of 50.0 m in 5 s.

d=1/2 at^2=1/2(4m/s^2)(5s)^2

With a somewhat downward push, the table would press _______ against the floor (as if it were heavier).

harder

An object that has twice as much mass as another object also has twice as much inertia. velocity. volume. gravitational acceleration. all of the above

inertia.

A car traveling at 100 km/h strikes an unfortunate bug that splatters on the windshield. The force of impact is greater on the bug. car. same for both

same for both

A ball is thrown straight up with enough speed so that it is in the air for several seconds. Assume the positive direction is upwards. Part complete What is the velocity of the ball when it reaches its highest point?

v = 0 m/s

A ball is thrown straight up with enough speed so that it is in the air for several seconds. Assume the positive direction is upwards. What is its velocity 0.70 s before it reaches its highest point?

v = 7.0 m/s

The weight of an object is the product of its mass, m, and the acceleration of gravity, g (where g=9.8 m/s2). If an object's mass is m=10. kg, what is its weight?

weight = 98 kg⋅m/s^2

The net force on any object moving at constant velocity is

zero.

A ball is thrown straight up with enough speed so that it is in the air for several seconds. Assume the positive direction is upwards. What is the change in velocity, v, during the 1.4-s interval from 0.70 s before the highest point to 0.70 s after the highest point? (Caution: We are talking about velocity, not speed.).

Δv = -14 m/s

A ball is thrown straight up with enough speed so that it is in the air for several seconds. Assume the positive direction is upwards What is the change in its velocity, v, during this 0.70-s interval?

Δv = -7.0 m/s

What is the acceleration of a Tesla automobile that maintains a constant velocity of 150 km/h?

0 m/s^2

The heavyweight boxing champion of the world punches a sheet of paper in midair, bringing it from rest up to a speed of 26.0 m/s in 0.052 s . The mass of the paper is 0.003 kg. Find the force of the punch on the paper.

F = 1.5 N

Find the strength of the net force produced by a 20-N force and a 12-N force in each of these cases. Both forces act in the same direction.

F = 32 N

If you stand next to a wall on a frictionless skateboard and push the wall with a force of 50 N , how hard does the wall push on you?

F = 50 N

Find the net force produced by a 32-N force and a 25-N force in each of these cases. The two forces act in opposite directions.

F = 7.0 N

A boxer can hit a heavy bag with great force. Why can't he hit a sheet of tissue paper in midair with the same amount of force?

The low mass of the tissue paper limits the amount of force the paper can exert on the boxer, and the forces between the boxer and paper must be equal and opposite.

We know that Earth pulls on the Moon. Does it follow that the Moon also pulls on Earth? -Yes, both pulls make up an interaction; neither can exist without the other. -No, if the Moon pulled on the Earth, the Earth would orbit the Moon.

Yes, both pulls make up an interaction; neither can exist without the other.

A force F acts in the forward direction on a cart of mass m. A friction force f opposes this motion. If the cart's mass is 4.4 kg , the applied force is 11.0 N , and the friction force is 5.2 N , find the cart's acceleration.

a = 1.3 m/s^2

Sophia exerts a steady 46-N horizontal force on a 8.8-kg box resting on a lab bench. The box slides against a horizontal friction force of 25 N. Find the box acceleration.

a = 2.4 m/s^2

Find the acceleration of a hamster when it increases its velocity from rest to 7.0 m/s in 2.6 s .

a = 2.7 m/s^2

Madison pushes with a 210-N horizontal force on a 20-kg crate of coffee resting on a warehouse floor. The force of friction on the crate is 84 N. Find the acceleration.

a = 6.3 m/s^2