EXAM 2
A 10-N block and a 1-N block lie on a horizontal frictionless table. To impart equal horizontal accelerations, we would have to push the heavier block with
10 times as much force.
A push on a 1-kg brick accelerates it. Neglecting friction, equally accelerating a 10-kg brick requires
10 times as much force.
When a baseball player bats a ball with a force of 1000 N, the reaction force that the ball exerts against the bat is
1000 N.
A bag of groceries that has a mass of 10 kilograms weighs about
100N
A 1-kg ball is thrown at 10 m/s straight upward. Neglecting air resistance, the net force that acts on the stone when it is halfway to the top of its path is about
10N
A 1-kg mass at the Earth's surface weighs
10N
A 1-kg rock that weighs 10 N is thrown straight upward at 20 m/s. Neglecting air resistance, the net force that acts on it when it is half way to the top of its path is
10N
The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is
10N
The mass of a lamb that weights 110 N is about
11kg
A tow truck exerts a force of 3000 N on a car, which then accelerates at 2 m/s2. What is the mass of the car?
1500 kg
The mass of a pet turtle that weighs 10 N is about
1kg
A jumbo jet has a mass of 100,000 kg. The thrust for each of its four engines is 50,000 N. What is the jet's acceleration when taking off?
2 m/s2
A car has a mass of 1000 kg and accelerates at 2 m/s2. What net force is exerted on the car?
2000 N
A car traveling at 22 m/s comes to an abrupt halt in 0.1 second when it hits a tree. What is the deceleration of the car?
220 m/s2
An astronaut of mass 70 kg weighs 700 N on Earth's surface. His weight on the surface of Mars, where the acceleration due to gravity is 3.7 m/s2, would be about
260 N.
Nellie pulls on a 10-kg wagon with a constant horizontal force of 30 N. If there are no other horizontal forces, what is the wagon's acceleration?
3.0 m/s2
A 2000-kg car experiences a braking force of 10,000 N and skids to a stop in 6 seconds. The speed of the car just before the brakes were applied was
30 m/s
A 500-N parachutist opens his chute and experiences an air resistance force of 800 N. The net force on the parachutist is then
300 N upward.
When a karate chop breaks a board with a 3000-N blow, the amount of force that acts on the hand is
3000 N.
If you are driving at 20 m/s and slam on your brakes and skid at 0.5g to a full stop, the skidding time is about
4 s
Scotty Skydiver of mass 100 kg experiences air resistance of 500 N, and an acceleration of about
0.5 g
You stand on your skateboard and exert a 50-N push on the wall next to you. If your mass is 60 kg you'll momentarily accelerate from the wall at about
0.8 m/s2.
A 10-N falling object encounters 10 N of air resistance. The net force on the object is
0N
An apple weighs 1 N. When the apple is held at rest above your head, the net force on the apple is
0N
Joshua is attracted toward Earth by a 500-N gravitational force. The Earth is attracted toward Joshua with a force of
500 N.
Phil stands at rest with both feet on a scale that reads 500 N. When he gently lifts one foot, the scale reads
500 N.
A mobile phone is pulled northward by a force of 10 N and at the same time pulled southward by another force of 15 N. The resultant force on the phone is
5N
A 10-N falling object encounters 4 N of air resistance. The net force on the object is
6N
A block is dragged without acceleration in a straight-line path across a level surface by a force of 6 N. What is the force of friction between the block and the surface?
6N
A pair of air pucks on an air table are set in motion when a compressed spring between them is released. If one puck moves with twice the speed of the other, then its mass is
half the mass of the other.
If the mass of a cart is quickly loaded to have twice the mass while a propelling force remains constant, the cart's acceleration
halves
A skydiver's terminal velocity will be greatest if she falls
head first
Two objects of the same size, but unequal weights are dropped from a tall tower. Taking air resistance into consideration, the object to hit the ground first will be the
heavier object
Nellie's weight and normal force usually have the same magnitude when she stands on a
horizontal surface.
When the bottom string is pulled slowly in the heavy-ball-and-strings demonstration (Figure 4.8 in your book), tension
in the top string is due to your pull plus the weight of the ball.
If an object's mass is decreasing while a constant force is applied to the object, the acceleration
increases
For every action force, there must be a reaction force that
is equal in magnitude.
A heavy block at rest is suspended by a vertical rope. When the block accelerates upward by the rope, the rope tension
is greater than its weight.
If the net force on a cart is tripled, the cart's acceleration
is three times as much
Whenever the net force on an object is zero, its acceleration
is zero
The mass of a rocket decreases as it burns through its fuel. If the rocket engine produces constant force (thrust), how does the acceleration of the rocket change over time?
it increases
A pair of toy freight cars, one twice the mass of the other, fly apart when a compressed spring that joins them is released. Acceleration will be greater for the
lighter car.
A rock is thrown vertically into the air. At the top of its path the net force on it is
mg
Which has zero acceleration? An object
moving at constant velocity, at rest, in mechanical equilibrium.
To produce an acceleration to a system there
must be a net force on the system.
Free fall is motion in which gravity is the only force acting. Is a skydiver who has reached terminal speed in free fall?
no
If a motorcycle moves with a constant acceleration, can you conclude that there is no net force acting on it?
no
Since an object weighs less on the surface of the Moon than on Earth's surface, does it have less inertia on the Moon's surface?
no
A car by itself is capable of a certain maximum acceleration. When it tows a car of the same mass, its maximum acceleration is
one half
When you walk, you push on the floor to the left and the floor
pushes you to the right.
The force exerted on the tires of a car that directly accelerate it along a road is exerted by the
road
Two factors that greatly affect air resistance on falling objects are frontal area and
speed
When a cannonball is fired from a cannon, which undergoes the greater acceleration?
the cannonball
The winner in a tug-of-war exerts the greatest force on
the ground.
A light woman and a heavy man jump from an airplane at the same time and open their same-size parachutes at the same time. Which person will get to the ground first?
the heavy man
A force of 1 N accelerates 1-kg box at the rate of 1 m/s2. The acceleration of a 2-kg box by a net force of 2 N is
the same
Compared to the mass of an apple on Earth, the mass of the apple on the Moon is
the same
A car traveling at 100 km/h strikes an unfortunate bug and splatters it. The force of impact is
the same for both.
An automobile and a golf cart traveling at the same speed collide head-on. The impact force is
the same for both.
To say there is no such thing as only one force means
there must also be a corresponding reaction force.
Earth pulls on the Moon, and the Moon pulls on Earth, which tells us that
these two pulls comprise an action-reaction pair.
Recall Galileo's Leaning Tower experiment. With negligible air resistance, a heavy and a light object fall
to the ground in equal times.with the same increases in speed. with equal accelerations.
A heavy ball hangs by a string, with a second string attached to its bottom. A slow pull on the bottom string breaks the
top string
You cannot exert a force on a wall
unless the wall simultaneously exerts the same amount of force on you.
When a parachutist opens her parachute after reaching terminal speed, in what direction does she accelerate?
up
If a motorcycle moves with a constant velocity, can you conclude that there is no net force acting on it?
yes
Is a satellite above the atmosphere that circles Earth in free fall?
yes
When a falling object has reached its terminal velocity, its acceleration is
zero
A boulder following a straight-line path at constant velocity has
zero acceleration.
A kilogram is a measure of an object's
a mass
If more horizontal force is applied to a sliding object than is needed to maintain a constant velocity, the object
accelerates in the direction of the applied force.
Your friend says that the heavyweight champion of the world cannot exert a force of 50 N on an isolated piece of tissue paper with his best punch. You
agree that it can't be done.
Action and reaction pairs of forces
always act simultaneously.
Which has the greater mass?
an automobile battery
At equilibrium on a bathroom weighting scale, the downward pull of gravity on you is balanced by
an upward support force
Art museums use weaker wires than those used in homes because paintings in museums
are suspended by pairs of vertical wires.
An archer shoots an arrow. Consider the action force to be the bowstring against the arrow. The reaction to this force is the
arrow's push against the bowstring.
Neglecting friction, a small and a large block of ice begin sliding down an incline together. The larger block reaches the bottom
at the same time as the small block.
A sack of potatoes weighing 200 N falls from an airplane. As the velocity of fall increases, air resistance also increases. When air resistance equals 200 N, the sack's acceleration becomes
0 m/s2.
In the video, forces acting on the car that are parallel to the direction of motion are analyzed. How are these forces related?
The forces are equal in size, act in opposite directions, and produce a zero net force.
What happens to the weight reading on a scale you stand on when you toss a heavy object upward?
The scale reading will increase during the throw.
A Mack truck and a Volkswagen traveling at the same speed have a head-on collision. The vehicle that undergoes the greatest change in velocity will be the
Volkswagen.
Newton's second law relates an object's acceleration to its mass and the net force acting on it. Does Newton's second law apply to a situation in which there is no net force? Select the best explanation.
Yes. The law applies and it tells us that the object has constant velocity.
As a ball falls, the action force is the Earth's pull on the ball. The reaction force is the
ball's pull on Earth.
Arnold Strongman and Suzie Small each pull very hard on opposite ends of a rope in a tug-of-war. The greater force on the rope is exerted by
both the same, interestingly.
A heavy ball hangs by a string, with a second string attached to its bottom (Figure 4.8 in your book). A quick pull on the bottom string breaks the
bottom string
When you rub your hands together, you
cannot push harder on one hand than the other.
You drive your car at a constant 60 km/h along the highway. You apply the brakes until the car slows to 40 km/h. If at that moment you suddenly release the brakes, the car tends to
continue moving at 40 km/h.
Nellie tosses a ball upward at an angle. Neglecting air resistance, the vertical component of the initial velocity
decreases with time to reach the top.
The force that propels a cannonball when fired from a cannon is
equal and opposite to the force the ball exerts on the cannon.
The force with which Earth pulls on the Moon is
equal in magnitude to the force that Moon pulls on Earth.
If less horizontal force is applied to a sliding object than is needed to maintain a constant velocity, the object
eventually slides to a stop.
When a rocket forces exhaust gases downward, the exhaust gases
exert an upward force on the rocket.
When a boxer hits a punching bag, the strength of his punch depends on how much force the bag can
exert on the boxer's fist.
The force that accelerates the orange and apple system featured in your textbook is actually supplied by the
floor
When you drop a rubber ball on the floor it bounces back. The force exerted on the ball to produce bouncing is by the
floor
The newton is a unit of
force
A player hits a ball with a bat. If action is the force of the bat against the ball, reaction is the
force that the ball exerts on the bat.
A player catches a ball. If action is the force of the ball against the player's glove, reaction is the
glove against the ball.
A coconut and a bird's feather fall from a tree through the air to the ground below. The force of air resistance is
greater on the coconut
