Deck 4: Forces and Newtons Laws of Motion

Question 1

A 27 kg object is accelerated at a rate of 1.7 m/s².What force does the object experience?

A)46 N
B)16 N
C)63 N
D)98 N

Answer 1

46 N

Question 2

The figure shows two forces of equal magnitude acting on an object.If the common magnitude of the forces is 4.6 N and the angle between them is 40°,what third force will cause the object to be in equilibrium?

A)8.6 N pointing to the right
B)7.0 N pointing to the right
C)4.3 N pointing to the right
D)3.5 N pointing to the right

Answer 2

8.6 N pointing to the right

Question 3

The figure shows an acceleration-versus-force graph for three objects pulled by rubber bands.The mass of object 2 is 36 kg.What are the masses of objects 1 and 3?

A)14 kg and 90 kg
B)72 kg and 18 kg
C)90 kg and 18 kg
D)14 kg and 72 kg

Answer 3

14 kg and 90 kg

Question 4

The figure shows an acceleration-versus-force graph for a 125 g object.What should be the value of the first tick-mark on the vertical scale?

A)4
B)8
C)0.00400
D)0.00800

Question 5

Two children fighting over a toy pull on the toy in different directions.One child pulls to the north with a force of 5.3 N,and the other child pulls to the east with a force of 6.3 N.What is the magnitude of the net force on the toy?

A)8.2 N
B)12 N
C)1.0 N
D)9.3 N

Question 6

The figure shows two forces acting on an object,with magnitudes F₁ = 78 N and F₂ = 26 N.What third force will cause the object to be in equilibrium?

A)52 N pointing down
B)52 N pointing up
C)82 N pointing down
D)82 N pointing up

Question 7

A child pulls on a wagon handle at an angle 37° above the horizontal with a force of 45 N.If the wagon accelerates at 8.1 m/s² horizontally,what is the mass of the wagon? Assume frictional forces are negligible.

A)4.4 kg
B)5.6 kg
C)3.1 kg
D)3.7 kg

Question 8

The figure shows two forces acting on an object.They have magnitudes F₁ = 6.3 N and F₂ = 2.1 N.What third force will cause the object to be in equilibrium?

A)6.6 N at 162° counterclockwise from
B)6.6 N at 108° counterclockwise from
C)4.2 N at 162° counterclockwise from
D)4.2 N at 108° counterclockwise from

Question 9

An object accelerates at 7.0 m/s² under the action of two rubber bands.What will be the acceleration of two of these objects glued together if they are pulled by four rubber bands?

A)7.0 m/s²
B)14 m/s²
C)28 m/s²
D)3.5 m/s²

Question 10

A Ferrari accelerates from 0 to 100.0 km/h in 4.80 s.What force (in Newtons)does a passenger of mass 68.0 kg experience during acceleration?

A)394 N
B)82.0 N
C)342 N
D)311 N

Question 11

A 1100 kg car traveling at 27 m/s starts to decelerate and comes to a complete stop in 578.0 m.What is the average braking force acting on the car?

A)-690 N
B)-550 N
C)-410 N
D)-340 N

Question 12

Under the action of a constant force an object accelerates at 7.8 m/s².What will the acceleration be if (a)The force is halved? (b)The object's mass is halved? (c)The force and the object's mass are both halved? (d)The force is halved and the object's mass is doubled?

A)(a)3.9 m/s², (b)16 m/s², (c)7.8 m/s², (d)2.0 m/s²
B)(a)16 m/s², (b)3.9 m/s², (c)2.0 m/s², (d)7.8 m/s²
C)(a)3.9 m/s², (b)16 m/s², (c)2.0 m/s², (d)7.8 m/s²
D)(a)3.9 m/s², (b)16 m/s², (c)7.8 m/s², (d)7.8 m/s²

Question 13

The figure shows an object's acceleration-versus-force graph.What is the object's mass in grams?

A)2.5
B)1.6
C)630
D)400,000

Question 14

Two forces act on a 55 kg object.One force has magnitude 65 N directed 59° clockwise from the positive x-axis,and the other has a magnitude 35 N at 32° clockwise from the positive y-axis.What is the magnitude of this object's acceleration?

A)1.1 m/s²
B)1.3 m/s²
C)1.5 m/s²
D)1.7 m/s²

Question 15

The engine of a 1250 kg car provides a forward directed force of 3651 N.If the car accelerates at a rate of 2.60 m/s²,what is the total resistive force (wind resistance,friction,etc. )acting on the car?

A)401 N
B)8600 N
C)2400 N
D)485 N

Question 16

It takes 4500 N to accelerate a car at a rate of 3.42 m/s².What is the mass of the car?

A)1310 kg
B)1700 kg
C)1510 kg
D)1040 kg

Question 17

A child on a sled starts from rest at the top of a 15.0° slope.If the trip to the bottom takes 15.2 s,how long is the slope? Assume that frictional forces may be neglected.

A)293 m
B)586 m
C)1130 m
D)147 m

Question 18

On its own,a tow truck has a maximum acceleration of 3.0 ms^-2.What would be the maximum acceleration when the truck was towing a bus of twice its own mass?

A)2.5 ms^-2
B)2.0 ms^-2
C)1.5 ms^-2
D)1.0 ms^-2

Question 19

Joe and Bill are playing tug-of-war.Joe is pulling with a force of 200 N.Bill is simply hanging on to the rope.Neither person is moving.What is the tension of the rope?

A)200 N
B)400 N
C)0 N
D)300 N

Question 20

An object accelerates at 4.1 m/s² under the action of two rubber bands.What will be the object's acceleration if it is pulled by four rubber bands?

A)8.2 m/s²
B)16 m/s²
C)4.1 m/s²
D)2.1 m/s²

Question 21

An elevator suspended by a vertical cable is moving downward but slowing down.The tension in the cable must be greater than the weight of the elevator.

Question 22

A satellite is in orbit around the earth.The satellite pulls just as hard on the earth as the earth pulls on the satellite.

Question 23

If a 5.0 kg box is pulled simultaneously by a 10.0 N force and a 5.0 N force,then its acceleration must be 3.0 m/s².

Question 24

If you pound a feather with a hammer,the feather always pushes on the hammer just as hard as the hammer pushes on the feather.

Question 25

In order to get an object moving,you must push harder on it than it pushes back on you.

Question 26

If the rockets of a spaceship in outer space (far from all gravity)suddenly lose power and go off,the spaceship will gradually slow to a stop.

Question 27

A bucket is being lowered by a rope with a constant downward acceleration.The tension in the rope must be equal to the weight of the bucket.

Question 28

In a collision between a huge SUV and a small compact car,the SUV exerts a larger force on the compact than the compact exerts on the SUV.

Question 29

When a small car is towing a large car by a very light (massless)horizontal rope,the rope exerts equal size forces on both cars.

Question 30

In order to lift a bucket of concrete,you must pull up harder on the bucket than it pulls down on you.

Question 31

A small car and an SUV are at a stoplight.The car has a mass equal to half that of the SUV,and the SUV's engine can produce a maximum force equal to twice that of the car.When the light turns green,both drivers floor it at the same time.Which vehicle pulls ahead of the other vehicle after a few seconds?

A)the car
B)the SUV
C)It is a tie.

Question 32

A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s.The vector sum of all the forces acting on this crate must point down the ramp.

Question 33

You pull on a crate with a rope.If the crate moves,the rope's pull on the crate must have been larger than the crate's pull on the rope,but if the crate does not move,both of these pulls must have been equal.

Question 34

You are in a train traveling on a horizontal track and notice that a piece of luggage starts to slide toward the front of the train.From this observation,you can conclude that this train is not an inertial reference frame because it is slowing down.

Question 35

Consider what happens when you jump up in the air.Which of the following is the most accurate statement?

A)It is the upward force exerted by the ground that pushes you up,but this force can never exceed your weight.
B)You are able to spring up because the earth exerts a force upward on you which is stronger than the downward force you exert on the earth.
C)Since the ground is stationary,it cannot exert the upward force necessary to propel you into the air.Instead,it is the internal forces of your muscles acting on your body itself which propels the body into the air.
D)When you push down on the earth with a force greater than your weight,the earth will push back with the same magnitude force and thus propel you into the air.

Question 36

A box is placed on a table which rests on the floor.The box pushes on the table;the reaction force to the box's push on the table is the table's push on the floor.

Question 37

Three children pull on a toy in three different directions,yet the toy does not move.Explain how this could be possible.

Question 38

An object is moving to the right in a straight line.The net force acting on the object is also directed to the right,but the magnitude of the force is decreasing with time.The object will

A)continue to move to the right,with its speed increasing with time.
B)continue to move to the right,with its speed decreasing with time.
C)continue to move to the right with a constant speed.
D)stop and then begin moving to the left.

Question 39

While flying horizontally in an airplane,you notice that a string dangling from the luggage compartment hangs at rest at 15 degrees away from the vertical.Using this observation,you can conclude that the airplane is an inertial reference frame because the string is not moving.

Question 40

You throw a stone vertically upward,and it feels no air resistance.Once it is free of your hand but moving upward,the two forces acting on it are the downward pull of gravity and the upward force due to its motion.

Question 41

Suppose the force of wind resistance is proportional to the speed of the object and in the direction opposite the object's velocity.If you throw an object upward,when is the magnitude of the acceleration the highest?

A)It is highest right after the object is released.
B)It is highest at the top of its trajectory.
C)The acceleration of the object is the same throughout the entire trajectory.

Question 42

Two bodies P and Q on a perfectly smooth horizontal surface are connected by a light cord.The mass of P is greater than that of Q.A horizontal force is applied to Q as shown in the figure,accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P will be

A)zero.
B)less than F but not zero.
C)equal to F.
D)greater than F.

Question 43

A large truck collides head-on with a cyclist.During the collision

A)the truck exerts the same amount of force on the cyclist as the cyclist exerts on the truck.
B)the truck exerts a greater amount of force on the cyclist than the cyclist exerts on the truck.
C)the truck exerts a smaller amount of force on the cyclist than the cyclist exerts on the truck.
D)the truck exerts a force on the cyclist,but the cyclist exerts no force on the truck.

Question 44

If you jumped out of a plane,you would begin speeding up as you fall downward.Eventually,due to wind resistance,your velocity would become constant with time.After this occurs,the magnitude of the force of wind resistance is

A)equal to the force of gravity acting on you.
B)is much smaller than the force of gravity acting on you.
C)is slightly smaller than the force of gravity acting on you.
D)is greater than the force of gravity acting on you.

Question 45

Suppose you are playing hockey on a new-age ice surface in which there is no friction between the ice and the hockey puck.You wind up and hit the puck as hard as you can.Just after the puck loses contact with your stick,the puck

A)will not slow down or speed up.
B)will start to slow down.
C)will speed up a little,and then slow down.
D)will speed up a little,and then move at a constant speed.

Question 46

When decelerating quickly in a car,you feel as if you are being thrown forward in your seat.Which one of Newton's Laws most directly explains this effect? Explain your reasoning.

Question 47

A dog is standing in the tail bed of a pickup truck.The tail bed is coated with ice,causing the force of friction between the dog and the truck to be zero.The truck is initially at rest,and then accelerates to the right,moving along a flat road.As seen from a stationary observer (watching the truck move to the right),the dog

A)does not move left or right,but simply slides toward the back of the truck.
B)moves to the right,but not as quickly as the truck is moving to the right,causing it to slide toward the back of the truck.
C)moves to the right at the same rate as the truck,so it doesn't slide.
D)moves to the left,as the truck moves to the right,causing the dog to slide toward the back of the truck.

Question 48

An object is moving with a constant velocity.Which statement(s)MUST be true?

A)The net force on the object is zero.
B)A small net force is acting on the object,in the direction of motion.
C)No forces are acting on the object.
D)Two of the above statements are true.

Question 49

A person gives a shopping cart an initial push along a horizontal floor to get it moving,and then lets go.The cart travels forward along the floor,gradually slowing as it moves.Consider the horizontal force(s)on the cart while it is moving forward and slowing.Which of the following statements is correct?

A)Both a forward and a backward force are acting on the cart,but the forward force is larger.
B)Both a forward and a backward force are acting on the cart,but the backward force is larger.
C)Only a forward force is acting,which diminishes with time.
D)Only a backward force is acting,no forward force.

Question 50

You are making a circular turn in your car when you hit a big patch of ice,causing the force of friction between the tires and the road to become zero.While the car is on the ice,it

A)moves along a straight-line path.
B)continues to follow a circular path,but with a radius larger than the original radius.
C)moves along a path that is neither straight nor circular.
D)continues to follow the same circular path as initially.

Question 51

In outer space,an astronaut is working with two pieces of equipment that are outwardly identical.However,one of the objects has a slightly larger mass than the other.Since objects are weightless in space,how can the astronaut distinguish between the two objects?

Question 52

Your younger brother is supposed to mow the lawn using a push mower.He reasons from Newton's Third Law that the mower will push back with the same force he exerts on the mower;therefore nothing will move and attempting to mow the lawn is pointless.What is wrong with his reasoning?

Question 53

Explain,in terms of Newton's Laws,why a quick jerk on a string may cause it to break,while the same change in momentum performed over a longer time will not.

Question 54

Newton's Third Law suggests that a book sitting on a flat table experiences an upward force due to the table.If this is true,why doesn't the book start moving upward?

Question 55

A ball is tossed vertically upward.When it reaches its highest point (before falling back downward),

A)the velocity is zero,the acceleration is directed downward,and the force of gravity acting on the ball is directed downward.
B)the velocity is zero,the acceleration is zero,and the force of gravity acting on the ball is zero.
C)the velocity is zero,the acceleration is zero,and the force of gravity acting on the ball is directed downward.
D)None of the above

Question 56

An object is moving to the right,and experiencing a net force that is directed to the right.The magnitude of the force is decreasing with time.The speed of the object is

A)increasing.
B)decreasing.
C)constant in time.

Question 57

A woman is straining to lift a large crate,without success.It is too heavy.We denote the forces on the crate as follows: P is the upward force being exerted on the crate by the person,C is the contact force on the crate by the floor,and W is the weight of the crate. How are the magnitudes of these forces related,while the person is trying unsuccessfully to lift the crate?

A)P + C = W
B)P + C < W
C)P + C > W
D)P = C

Question 58

A ball is thrown vertically upward,reaches a highest point,and comes back down.At the top of its path,what forces,if any,act on the ball? Explain your answer.

A)no forces
B)only a downward force
C)only an upward force
D)an upward and a downward force,opposing and equal

Question 59

Bill and Susan are both standing on identical skateboards (with really good ball bearings),initially at rest.Bill weighs three times as much as Susan.Bill pushes horizontally on Susan's back,causing Susan to start moving away from Bill.Immediately after Bill stops pushing,

A)Susan and Bill are moving away from each other,and Susan's speed is three times that of Bill.
B)Susan is moving away from Bill,and Bill is stationary.
C)Susan and Bill are moving away from each other,with equal speeds.
D)Susan and Bill are moving away from each other,and Susan's speed is three times less than that of Bill.

Question 60

A stalled car is being pushed up a hill by three people,and it is moving at a constant speed.The net force on the car is

A)zero.
B)in the same direction of the car's motion.
C)in the opposite direction of the car's motion.
D)None of the above