Physics 100 - Week 3: Knowledge Check

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? a. 0.3 m/s2 b. 3.0 m/s2 c. 10 m/s2 d. 300 m/s2 e. 30 m/s2

b. 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 a. 15 m/s. b. 30 m/s. c. 45 m/s. d. None of these e. 1.2 m/s.

b. 30 m/s.

A 300-kg bear grasping a vertical tree slides down at constant velocity. The friction force between the tree and the bear is a. 300 N. b. 3000 N. c. 30 N. d. more than 3000 N.

b. 3000 N.

An astronaut on another planet drops a 1-kg rock from rest and finds that it falls a vertical distance of 2.5 meters in one second. On this planet, the rock has a weight of a. 2 N. b. 5 N. c. 4 N. d. 3 N. e. 1 N.

b. 5 N.

A 10-kilogram block with an initial velocity of 10 m/s slides 10 meters across a horizontal surface and comes to rest. It takes the block 2 seconds to stop. The stopping force acting on the block is about a. None of these b. 50 N. c. 5 N. d. 25 N. e. 10 N.

b. 50 N.

If more horizontal force is applied to a sliding object than is needed to maintain a constant velocity, the object a. experiences greater friction. b. accelerates in the direction of the applied force. c. None of these d. accelerates opposite the direction of the applied force.

b. accelerates in the direction of the applied force.

A constant net force on a rail-road car produces constant a. both of these b. acceleration. c. velocity. d. neither of these

b. acceleration.

A rock is thrown vertically into the air. At the top of its path the net force on it is a. less than mg. b. mg. c. more than mg.

b. mg.

A car by itself is capable of a certain maximum acceleration. When it tows a twice-as-massive car, its maximum acceleration is a. the same. b. one third. c. one fourth. d. one half. e. none of these

b. one third.

A car has a mass of 1000 kg and accelerates at 2 m/s2. What net force is exerted on the car? a. 500 N b. 1000 N c. 2000 N d. none of these e. 1500 N

c. 2000 N

The newton is a unit of a. inertia. b. density. c. force. d. mass.

c. force.

If an object's mass is decreasing while a constant force is applied to the object, the acceleration a. decreases. b. remains the same. c. increases.

c. increases.

If the net force on a cart is tripled, the cart's acceleration a. is more than three times as much. b. is one third. c. is three times as much. d. is two thirds.

c. is three times as much.

A skydiver steps from a helicopter and falls for a few seconds until terminal velocity is reached. Thereafter, until he opens his parachute, his acceleration a. None of these b. decreases. c. is zero. d. is constant. e. increases.

c. is zero.

Two tennis balls fall through the air from a tall building. One of them is filled with lead pellets. The ball to reach the ground first is the a. regular ball. b. same for both c. lead-filled ball.

c. lead-filled ball.

A kilogram is a measure of an object's a. both of these b. force. c. mass. d. neither of these

c. mass.

A ball is thrown vertically into the air. Because of air resistance, its time coming down compared to its time going up is a. the same. b. less. c. more.

c. more.

A 500-N parachutist opens his chute and experiences an air resistance force of 800 N. The net force on the parachutist is then a. 500 N downward. b. 800 N downward. c. 500 N upward. d. 300 N upward. e. 300 N downward.

d. 300 N upward.

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 a. 0 N. b. 25 N. c. 150 N. d. 5 N.

d. 5 N.

Suzie Skydiver, who weighs 500 N, reaches terminal velocity of 90 km/h. The air resistance on Suzie is then a. 90 N. b. 250 N. c. 410 N. d. 500 N. e. None of these

d. 500 N.

A 10-N falling object encounters 10 N of air resistance. The net force on the object is a. 4 N. b. 6 N. c. 0 N. d. none of these e. 10 N.

c. 0 N.

A 1-kg mass at the Earth's surface weighs a. 10 N. b. 12 N. c. None of these d. 1 N. e. 5 N.

a. 10 N.

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 a. 10 N. b. less than 10 N. c. more than 10 N.

a. 10 N.

A 10-kg brick and a 1-kg apple are dropped in a vacuum. The force of gravity on the brick is a. 10 times more than the force on the apple. b. zero. c. the same as the force on the apple. d. one-tenth as much as on the apple.

a. 10 times more than the force on the apple.

The mass of a lamb that weights 110 N is about a. 11 kg. b. 110 kg. c. 1100 kg. d. 1 kg. e. None of these

a. 11 kg.

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? a. 220 m/s2 b. 110 m/s2 c. 800 m/s2 d. 880 m/s2 e. need more information

a. 220 m/s2

Phil stands at rest with both feet on a scale that reads 500 N. When he gently lifts one foot, the scale reads a. 500 N. b. less than 500 N. c. more than 500 N.

a. 500 N.

Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has the same a. None of these b. All of these c. mass. d. weight. e. volume.

a. None of these

Which has the greater mass? a. an automobile battery b. both the same c. a king-size pillow

a. an automobile battery

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 a. bottom string. b. top string. c. top or bottom string equally.

a. bottom string.

Suppose a particle is being accelerated through space by a 10-N force. Suddenly the particle encounters a second force of 10 N in the opposite direction. The particle with both forces acting a. continues at the speed it had when it encountered the second force. b. decelerates gradually to a halt. c. theoretically tends to accelerate toward the speed of light. d. is brought to a rapid halt. e. None of these

a. continues at the speed it had when it encountered the second force.

If the mass of a cart is quickly loaded to have twice the mass while a propelling force remains constant, the cart's acceleration a. halves. b. quadruples. c. stays the same. d. doubles. e. none of these

a. halves.

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 a. heavier object. b. lighter object. c. not enough information d. Both hit at the same time.

a. heavier object.

If a non-rotating object has no acceleration, then we can say for certain that it is a. in mechanical equilibrium. b. All of these c. None of these d. moving at constant non-zero velocity. e. at rest.

a. in mechanical equilibrium.

An object with twice as much mass as another object has twice as much a. inertia. b. All of these c. speed. d. acceleration due to gravity.

a. inertia.

Whenever the net force on an object is zero, its acceleration a. is zero. b. may be more than zero. c. may be less than zero.

a. is zero.

A ball thrown straight upward takes 10 seconds for its up-and-down round trip. Because of air resistance, the time taken for the ball just to go up is a. less than 5 s. b. more than 5 s. c. 5 s.

a. less than 5 s.

A ball is thrown vertically into the air. Because of air resistance, its speed when it returns to its starting level compared with its initial speed is a. less. b. the same. c. more.

a. less.

An object's weight is properly expressed in units of a. newtons. b. kilograms. c. cubic centimeters. d. meters.

a. newtons.

A bowling ball and a baseball accelerate equally when falling in a vacuum because a. the ratio of their weights to mass is the same. b. the force of gravity does not act in a vacuum. c. their velocities are the same. d. the force of gravity is the same for each in a vacuum. e. None of these

a. the ratio of their weights to mass is the same.

A heavy ball hangs by a string, with a second string attached to its bottom. A slow pull on the bottom string breaks the a. top string. b. bottom string. c. top or bottom string equally.

a. top string.

When a falling object has reached its terminal velocity, its acceleration is a. zero. b. constant. c. g.

a. zero.

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 a. 10 m/s2. b. 0 m/s2. c. infinite. d. None of these e. 5 m/s2.

b. 0 m/s2.

A rock is thrown vertically into the air. At the top of its path, its acceleration is a. zero. b. 10 m/s2. c. between 0 and 10 m/s2. d. greater than 10 m/s2.

b. 10 m/s2.

A push on a 1-kg brick accelerates it. Neglecting friction, equally accelerating a 10-kg brick requires a. 100 times as much force. b. 10 times as much force. c. one-tenth the amount of force. d. None of these e. just as much force.

b. 10 times as much force.

A bag of groceries that has a mass of 10 kilograms weighs about a. 10 N. b. 100 N. c. 1000 N. d. 1 N. e. greater than 1000 N.

b. 100 N

In which case would you have the largest mass of gold? If your chunk of gold weighed 1 N on the a. Earth. b. Moon. c. planet Jupiter.

b. Moon.

If you double the net force on an object, you'll double its a. speed. b. acceleration. c. All of these d. velocity.

b. acceleration.

At equilibrium on a bathroom weighting scale, the downward pull of gravity on you is balanced by a. your mass. b. an upward support force. c. your weight.

b. an upward support force.

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 a. momentarily regain its higher initial speed. b. continue moving at 40 km/h. c. decrease in speed if no other forces act.

b. continue moving at 40 km/h.

A skydiver's terminal velocity will be greatest if she falls a. with her parachute open. b. head first. c. lying flat on her back. d. lying flat on her stomach.

b. head first.

A heavy rock and a light rock of the same size are falling through the air from a tall building. The one that encounters the greatest air resistance is the a. light rock. b. heavy rock. c. same for both

b. heavy rock.

When the bottom string is pulled slowly in the heavy-ball-and-strings demonstration (Figure 4.8 in your book), tension a. in the bottom string is zero. b. in the top string is due to your pull plus the weight of the ball. c. is about the same in both strings.

b. in the top string is due to your pull plus the weight of the ball.

A heavy block at rest is suspended by a vertical rope. When the block accelerates upward by the rope, the rope tension a. equals its weight. b. is greater than its weight. c. is less than its weight.

b. is greater than its weight.

A single brick falls with acceleration g. The reason a double brick falls with the same acceleration is a. None of these b. its ratio of force to mass is the same. c. that in free fall all accelerations are g. d. an experimental fact tested many times.

b. its ratio of force to mass is the same.

A ball is thrown upwards and caught when it returns. Compared with its initial speed and in the presence of air resistance, the speed with which it is caught is always a. the same. b. less. c. more. d. can't be determined.

b. less.

When you stand at rest with your left foot on one bathroom scale and your right foot on a similar scale, each of the scales will a. read your weight. b. show readings that when added equal your weight. c. read half your weight. d. cancel your weight.

b. show readings that when added equal your weight.

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 a. twice as much. b. the same. c. half as much. d. None of these

b. the same.

Compared to the mass of an apple on Earth, the mass of the apple on the Moon is a. one sixth as much. b. the same. c. six times as much. d. zero.

b. the same.

The brakes of a speeding truck are slammed on and it skids to a stop. If the truck were heavily loaded so that it had twice the total mass, the skidding distance would be a. half as far. b. the same. c. twice as far. d. 1.5 times as far. e. 4 times as far.

b. the same.

A boulder following a straight-line path at constant velocity has a. no forces acting on it. b. zero acceleration. c. a net force acting upon it in the direction of motion. d. None of these

b. zero acceleration.

Scotty Skydiver of mass 100 kg experiences air resistance of 500 N, and an acceleration of about a. greater than 0.5 g. b. 0.4 g. c. 0.5 g. d. 0.3 g. e. 0.2 g.

c. 0.5 g.

An apple at rest weighs 1 N. The net force on the apple when it is in free fall is a. None of these b. 9.8 N. c. 1 N. d. 0.1 N. e. 0 N.

c. 1 N.

The mass of a pet turtle that weighs 10 N is about a. 1000 kg. b. 100 kg. c. 1 kg. d. None of these e. 10 kg.

c. 1 kg.

A 10-kilogram block is pushed across a horizontal surface with a horizontal force of 20 N against a friction force of 10 N. The acceleration of the block is a. 2 m/s2. b. 10 m/s2. c. 1 m/s2. d. None of these e. 5 m/s2.

c. 1 m/s2.

A 1-kg ball is thrown at 10 m/s straight upward. Neglecting air resistance, the net force that acts on the ball when it is halfway to the top of its path is about a. 1/2 N. b. 5 N. c. 10 N. d. 1 N. e. 7.5 N.

c. 10 N.

The force of friction on a sliding object is 10 N. The applied force needed to maintain a constant velocity is a. more than 10 N. b. less than 10 N. c. 10 N.

c. 10 N.

An object released from rest on another planet requires one second to fall a distance of 6 meters. What is the acceleration due to gravity on this planet? a. None of these b. 15 m/s2 c. 12 m/s2 d. 6 m/s2 e. 3 m/s2

c. 12 m/s2

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? a. 0.25 m/s2 b. 1 m/s2 c. 2 m/s2 d. 4 m/s2 e. None of these

c. 2 m/s2

What horizontally-applied force will accelerate a 400-kg crate at 1 m/s2 across a factory floor against a friction force half its weight? a. 600 N b. None of these c. 2400 N d. 2000 N e. 1600 N

c. 2400 N

An astronaut on another planet drops a 1-kg rock from rest. The astronaut notices that the rock falls 2 meters straight down in one second. On this planet, how much does the rock weigh? a. 1 N b. 10 N c. 4 N d. 5 N

c. 4 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 a. greater than 6 s. b. 5 s. c. 4 s. d. 3 s. e. 6 s.

c. 4 s.

Compared to a 1-kg block of solid iron, a 2-kg block of solid iron has twice as much a. inertia. b. volume. c. All of these d. None of these e. mass.

c. All of these

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? a. The light woman b. Both should arrive at the same time. c. The heavy man d. not enough information

c. The heavy man

Neglecting friction, a small and a large block of ice begin sliding down an incline together. The larger block reaches the bottom a. before the small block. b. after the small block. c. at the same time as the small block.

c. at the same time as the small block.

Suzie Skydiver jumps from a high-flying plane. As her velocity of fall increases, her acceleration a. remains unchanged regardless of air resistance. b. increases. c. decreases.

c. decreases.

If less horizontal force is applied to a sliding object than is needed to maintain a constant velocity, the object a. None of these b. accelerates in the direction of the applied force. c. eventually slides to a stop. d. experiences decreased friction.

c. eventually slides to a stop.

A coconut and a bird's feather fall from a tree through the air to the ground below. The force of air resistance is a. greater on the feather. b. the same on each. c. greater on the coconut.

c. greater on the coconut.

Two factors that greatly affect air resistance on falling objects are frontal area and a. mass. b. weight. c. speed.

c. speed.

When a constant and sustained upward force acts on a rocket, its acceleration increases mainly because a. No way, for acceleration would be constant. b. gravity becomes weaker with increased distance. c. the mass of the rocket decreases as fuel is burned.

c. the mass of the rocket decreases as fuel is burned.

An apple weighs 1 N. When the apple is held at rest above your head, the net force on the apple is a. 0.1 N. b. 9.8 N. c. None of these d. 0 N. e. 1 N.

d. 0 N.

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? a. need more information b. more than 6 N c. less than 6 N d. 6 N

d. 6 N

Recall Galileo's Leaning Tower experiment. With negligible air resistance, a heavy and a light object fall a. with equal accelerations. b. with the same increases in speed. c. to the ground in equal times. d. All of these

d. All of these

Which has zero acceleration? An object a. at rest. b. None of these c. moving at constant velocity. d. All of these e. in mechanical equilibrium.

d. All of these

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 a state of zero acceleration first? a. Both should arrive at the same time. b. The heavy man c. not enough information d. The light woman

d. The light woman

If an apple experiences a constant net force, it will have a constant a. speed. b. position. c. velocity. d. acceleration. e. more than one of these

d. acceleration.

A large and a small person wish to parachute at equal terminal velocities. The larger person should a. pull upward on the supporting strands to decrease the downward net force. b. jump lightly. c. jump first from the plane. d. get a larger parachute.

d. get a larger parachute.

A car by itself is capable of a certain maximum acceleration. When it tows a car of the same mass, its maximum acceleration is a. one fourth. b. none of these c. one third. d. one half. e. the same.

d. one half.

Your weight as measured on your bathroom scale is a. a property of mechanical equilibrium. b. equal to your mass. c. All of these d. the force due to gravity on you.

d. the force due to gravity on you.

Strange as it may seem, it is just as difficult to accelerate a car on a level surface on the Moon as it is here on Earth because a. the weight of the car is independent of gravity. b. both of these c. neither of these d. the mass of the car is independent of gravity.

d. the mass of the car is independent of gravity.

A rock weighs 30 N on Earth and another rock weighs 30 N on the Moon. Which rock has the greater mass? a. the one on Earth b. They have the same mass. c. not enough information d. the one on the Moon

d. the one on the Moon

A feather and a coin will have equal accelerations when falling in a vacuum because a. the force of gravity is the same for each in a vacuum. b. the force of gravity does not act in a vacuum. c. their velocities are the same. d. the ratio of both the feather's and coin's weight to mass is the same. e. None of these

d. the ratio of both the feather's and coin's weight to mass is the same.

The force required to maintain a constant velocity for an astronaut in free space is equal to a. the force required to stop the astronaut. b. the weight of the astronaut. c. None of these d. zero. e. the mass of the astronaut.

d. zero.

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 a. None of these b. 1/10 as much force. c. an equal force. d. 10 squared or 100 times as much force. e. 10 times as much force.

e. 10 times as much force.

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? a. 1000 kg b. 500 kg c. none of these d. 3000 kg e. 1500 kg

e. 1500 kg

The human body can withstand an acceleration of 10 g under certain conditions. What net force would produce this acceleration for a 50-kg person? a. 2500 N b. 500 N c. 25,000 N d. None of these e. 5000 N

e. 5000 N

A 10-N falling object encounters 4 N of air resistance. The net force on the object is a. 4 N. b. 0 N. c. 10 N. d. None of these e. 6 N.

e. 6 N.