chapter5 Flashcards
How many forces are required for an interaction?
Two forces, an action and a reaction, are needed for an interaction
A Volkswagen Bug and a Volvo truck have a head-on collision. Which statement is true??
The magnitudes of both forces are the same
Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force?
Yes, you pull up on Earth with the same force
If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?
Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force.
Can you physically touch a person without that person touching you with the same amount of force?
No, when you touch a person, they must touch you with an equal and opposite force
How does the magnitude of the vertical component of velocity for a ball tossed at an upward angle change as the ball travels upward? How about the horizontal component of velocity when air resistance is negligible?
The vertical component decreases in magnitude until it reaches the maximum height and then increases; the horizontal component is constant.
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
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
When you walk, you push on the floor to the left and the floor
pushes you to the right
Harry pulls on the end of a spring attached to a wall. The reaction to Harry’s pull on the spring is
the spring pulling on Harry
Action and reaction pairs of forces
always act simultaneously
For every action force, there must be a reaction force that
is equal in magnitude
To produce an acceleration to a system there
must be a net force on the system
While you stand on the floor you are pulled downward by gravity, and supported upward by the floor. Gravity pulling down and the support force pushing up
do not make an action-reaction pair of forces.
The force exerted on the tires of a car that directly accelerate it along a road is exerted by the
road
Neglecting air resistance, once a tossed ball leaves your hand
only the force due to gravity acts on it.
An automobile and a golf cart traveling at the same speed collide head-on. The impact force is
the same for both.
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
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
The force with which Earth pulls on the Moon is
equal in magnitude to the force that Moon pulls on Earth
When a cannonball is fired from a cannon, which undergoes the greater acceleration?
the cannonball
The force that propels a cannonball when fired from a cannon is
equal and opposite to the force the ball exerts on the cannon
When a rocket forces exhaust gases downward, the exhaust gases
exert an upward force on the rocket
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
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
When Nellie hangs suspended from a pair of ropes that are not vertical, the tension in each rope is
more than half her weight
Nellie tosses a ball upward at an angle. Neglecting air resistance, the horizontal component of the initial velocity
remains constant
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 airspeed of an airplane is 200 km/h. When it is caught in a 200-km/h crosswind, its speed across the ground below is
283 km/h
A river 100 m wide flows due south. A boat that goes 1 m/s relative to the water is pointed due east as it crosses from the west bank. The boat crosses in
100 s
A river 100 m wide flows due south at 1 m/s. A boat that goes 1 m/s relative to the water leaves the west bank. To land at a point due east of its starting point, the boat must be pointed
nowhere it can’t be done.
Why does the vertical component of velocity for a projectile change with time, whereas the horizontal component of velocity doesn’t change?
Gravity is a purely vertical force
A stone is thrown upward at an angle. What happens to the horizontal component of its velocity as it rises? As it falls?
Rising or falling, it does not change.
A stone is thrown upward at an angle. What happens to the magnitude of the vertical component of its velocity as it rises? As it falls?
It decreases while rising, but it increases while falling
A ball rolls off the edge of a table at the same time another ball drops vertically from the same table. The ball to hit the floor first is the
both hit at the same time
As soon as a bowling ball rolls off the edge of a table its horizontal component of velocity
remains constant.
A Texas State Bobcat tosses a ball at an angle to the horizon such that the vertical component of velocity is 30 m/s and the horizontal component of velocity is 20 m/s. Neglect air resistance. About how far from the student does the ball land?
120 m
A vertical vector of 3 units combined with a horizontal vector of 4 units has a resultant of
5 units
