Deck 5: Applying Newtons Laws

Question 1

A 6.0 kg box is held at rest by two ropes that form 30° angles with the vertical.An external force F acts vertically downward on the box.The force exerted by each of the two ropes is denoted by T.A force diagram,showing the four forces that act on the box in equilibrium,is shown in the figure.The magnitude of force F is 410 N.The magnitude of force T is closest to:

A)271 N
B)235 N
C)188 N
D)376 N
E)470 N

Answer 1

271 N

Question 2

A piano mover raises a 100 kg piano at a constant rate using a frictionless pulley system,as shown in the figure.With roughly what force is the mover pulling down on the rope?

A)2000 N
B)1000 N
C)500 N
D)250 N
E)Depends on the velocity!

Answer 2

500 N

Question 3

A 6.0 kg box slides down an inclined plane that makes an angle of 39° with the horizontal.If the coefficient of kinetic friction is 0.19,at what rate does the box accelerate down the slope? (Use g = 9.8 m/s². )

A)4.7 m/s²
B)5.2 m/s²
C)5.5 m/s²
D)6.2 m/s²

Answer 3

4.7 m/s²

Question 4

Dick and Jane stand on a platform of negligible weight,as shown in the figure.Dick weighs 500 N and Jane weighs 400 N.Jane is supporting some of her weight on the end of the rope she is holding.What is the downward force she is exerting on the platform?

A)0
B)50 N
C)100 N
D)240 N
E)300 N

Question 5

A person with a mass of 78 kg is riding in an elevator that is accelerating upward at 1.80 m/s².What is the person's apparent weight? (Use g = 9.8 m/s². )

A)900 N
B)760 N
C)620 N
D)960 N

Question 6

What is the mass of an object that experiences a gravitational force of 685 N near Earth's surface?

A)69.9 kg
B)68.5 kg
C)71.3 kg
D)72.7 kg

Question 7

A 80 N force is needed to slide a 50.0 kg box across a flat surface at a constant velocity.What is the coefficient of kinetic friction between the box and the floor? (Use g = 9.8 m/s². )

A)0.16
B)0.13
C)0.15
D)0.18

Question 8

Kieran takes off down a 50 m high,10° slope on his jet-powered skis.The skis have a thrust of 280 N.The combined mass of skis and Kieran is 50kg (the fuel mass is negligible).Kieran's speed at the bottom is 40 m/s.What is the coefficient of kinetic friction of his skis on snow?

A)0.47
B)0.58
C)0.23
D)0.29

Question 9

A skydiver reaches a "terminal velocity" of 120 km/h.If the skydiver has a mass of 59.0 kg,what is the magnitude of the upward force on the skydiver due to wind resistance? (Use g = 9.8 m/s². )

A)578 N
B)6.02 N
C)5.42 N
D)636 N

Question 10

Jason takes off across level water on his jet-powered skis.The combined mass of Jason and skis is 75 kg (the mass of the fuel is negligible).The skis have a thrust of 200 N and a coefficient of kinetic friction on water of 0.1.Unfortunately,the skis run out of fuel after only 67 s.How far has Jason traveled when he finally coasts to a stop?

A)10,000 m
B)7600 m
C)5400 m
D)3800 m

Question 11

A 200 g hockey puck is launched up a metal ramp that is inclined at a 30° angle.The coefficients of static and kinetic friction between the hockey puck and the metal ramp are µs = 0.40 and µk = 0.30,respectively.The puck's initial speed is 63 m/s.What vertical height does the puck reach above its starting point?

A)130 cm
B)270 cm
C)200 cm
D)66 cm

Question 12

A 15 kg block is on a ramp that is inclined at 20° above the horizontal.It is connected by a string to a 19 kg mass that hangs over the top edge of the ramp.Assuming that frictional forces may be neglected,what is the magnitude of the acceleration of the 19 kg block? (See the figure. )

A)4.0 m/s²
B)3.8 m/s²
C)4.2 m/s²
D)4.5 m/s²

Question 13

A tightrope walker walks across a 30.0 m long wire tied between two poles.The center of the wire is displaced vertically downward by 1.0 m when he is halfway across.If the tension in both halves of the wire at this point is 6294 N,what is the mass of the tightrope walker? Neglect the mass of the wire.

A)85 kg
B)43 kg
C)74 kg
D)91 kg

Question 14

An object at rest on an inclined plane starts to slide when the incline angle is increased to 17°.What is the coefficient of static friction between the object and the incline? (Use g = 9.8 m/s². )

A)0.31
B)0.27
C)0.33
D)0.37

Question 15

A fish is to be weighed at the harbor.If the mass of the fish is 69.0 kg,what will be the reading on the scale? (Use g = 9.8 m/s². )

A)676 N
B)7.04 N
C)7.74 N
D)744 N

Question 16

Three blocks, connecting ropes, and a light frictionless pulley comprise a system, as shown. An external force P is applied downward on block A. The system accelerates at the rate of 2.5 m/s². The tension in the rope connecting block B and block C equals 60 N.
In the figure above,the external force P is closest to:

A)170 N
B)190 N
C)210 N
D)230 N
E)250 N

Question 17

You push downward on a trunk at an angle 25° below the horizontal with a force of 750 N.If the trunk is on a flat surface and the coefficient of static friction is 0.76,what is the most massive trunk you will be able to move? (Use g = 9.8 m/s². )

A)59 kg
B)68 kg
C)54 kg
D)82 kg

Question 18

Starting from rest,a 75 kg skier slides down a 17.0° slope.If the coefficient of kinetic friction between the skis and snow is 0.120 and it takes 16.9 s to get to the bottom,how long is the ski trail? (Use g = 9.8 m/s². )

A)248 m
B)496 m
C)124 m
D)186 m

Question 19

A device has a 100 g wooden shuttle that is pulled horizontally along a square frictionless wooden rail by an elastic band.The shuttle is released when the elastic band has 6.4 N tension at a 35º angle.What is the magnitude of the initial acceleration of the shuttle? (See the figure. )

A)52 m/s²
B)37 m/s²
C)64 m/s²
D)62 m/s²

Question 20

A 10.0 kg block on a table is connected by a string to a 63 kg mass,which is hanging over the edge of the table.Assuming that frictional forces may be neglected,what is the magnitude of acceleration of the 10.0 kg block when the other block is released? (See the figure. )

A)8.5 m/s²
B)8.1 m/s²
C)7.5 m/s²
D)9.0 m/s²

Question 21

Joe and Bill are playing tug-of-war.Joe is pulling with a force of 200 N.Bill is simply hanging on,but skidding toward Joe at a constant velocity.What is the force of friction between Bill's feet and the ground?

A)200 N
B)400 N
C)less than 200 N
D)greater than 200 N,but less than 400 N

Question 22

The figure shows two 1.0 kg blocks connected by a rope.A second rope hangs beneath the lower block.Both ropes have a mass of 250 g.The entire assembly is accelerated upward at 5.5 m/s² by force .What is the tension at the bottom end of rope 1?

A)19 N
B)23 N
C)38 N
D)6.9 N

Question 23

A 22 kg box must be slid across the floor.If the coefficient of static friction between the box and floor is 0.37,what is the minimum force needed to start the box moving from rest?

A)80 N
B)216 N
C)56 N
D)112 N

Question 24

The figure shows a 2000 kg cable car descending a high hill.A counterweight of mass 1800 kg on the other side of the hill aids the brakes in controlling the cable car's speed.The rolling friction of both the cable car and the counterweight are negligible.How much braking force does the cable car need to descend at constant speed?

A)3800 N
B)2900 N
C)2000 N
D)980 N

Question 25

A 75 pound box rests on a perfectly smooth horizontal surface.Any horizontal force greater than zero will cause it to start moving.

Question 26

The figure shows a block of mass m resting on a 20° slope.The block has coefficients of friction µs = 0.55 and µk = 0.45 with the surface.It is connected via a massless string over a massless,frictionless pulley to a hanging block of mass 2.0 kg.What is the minimum mass m that will stick and not slip?

A)2.3 kg
B)3.9 kg
C)1.4 kg
D)3.8 kg

Question 27

A person who normally weighs 200 pounds is standing on a scale inside an elevator.The elevator is moving upwards with a speed of 7 m/s,and then begins to slow down at a rate of 5 m/s².Before the elevator begins to slow down,the reading of the scale is _________,and while the elevator is slowing down,the reading of the scale is ________.

A)200 pounds,100 pounds
B)greater than 200 pounds,100 pounds
C)greater than 200 pounds,0 pounds
D)less than 200 pounds,100 pounds
E)None of the above

Question 28

If I weigh 741 N on Earth and 5320 N on the surface of a nearby planet,what is the acceleration due to gravity on that planet?

A)70.4 m/s²
B)51.4 m/s²
C)61.2 m/s²
D)81.0 m/s²

Question 29

Consider the following figure.Assume the strings and pulleys have negligible masses and the coefficient of kinetic friction between the 2.0 kg block and the table is 0.25.What is the acceleration of the 2.0 kg block?

A)2.5 m/s²
B)1.7 m/s²
C)3.2 m/s²
D)4.0 m/s²

Question 30

Jason takes off across level water on his jet-powered skis.The combined mass of Jason and skis is 75 kg (the mass of the fuel is negligible).The skis have a thrust of 200 N and a coefficient of kinetic friction on water of 0.1.Unfortunately,the skis run out of fuel after only 90 s.What is Jason's top speed?

A)150 m/s
B)240 m/s
C)24 m/s
D)90 m/s

Question 31

A 200 g hockey puck is launched up a metal ramp that is inclined at a 30° angle.The coefficients of static and kinetic friction between the hockey puck and the metal ramp are µs = 0.40 and µk = 0.30,respectively.The puck's initial speed is 16 m/s.What vertical height does the puck reach above its starting point?

A)8.6 cm
B)17 cm
C)13 cm
D)4.2 cm

Question 32

A rope pulls on the lower block in the figure with a tension force of 20 N.The coefficient of kinetic friction between the lower block and the surface is 0.16.The coefficient of kinetic friction between the lower block and the upper block is also 0.16.What is the acceleration of the 2.0 kg block?

A)6.9 m/s²
B)7.6 m/s²
C)8.4 m/s²
D)9.2 m/s²

Question 33

A wooden block A of mass 4.0 kg slides on a frictionless table when pulled via a massless string and pulley array by a hanging box B of mass 5.0 kg,as shown in the figure.What is the acceleration of block A as it slides on the frictionless table? Hint: Think carefully about the acceleration constraint.

A)4.1 m/s²
B)3.5 m/s²
C)3.1 m/s²
D)2.7 m/s²

Question 34

A 15,000 kg rocket blasts off from Earth with a uniform upward acceleration of 2.0 m/s2 and feels no air resistance.The thrust force its engines must provide during this acceleration is 30,000 N upward.

Question 35

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 36

The figure shows two 1.0 kg blocks connected by a rope.A second rope hangs beneath the lower block.Both ropes have a mass of 250 g.The entire assembly is accelerated upward at 2.3 m/s² by force .What is the tension at the top end of rope 1?

A)18 N
B)15 N
C)2.9 N
D)3.5 N

Question 37

A 100 g ball of clay is thrown horizontally with a speed of 50.0 m/s toward a 900 g block resting on a frictionless surface.It hits the block and sticks.The clay exerts a constant force on the block during the 10.0 ms it takes the clay to come to rest relative to the block.After 10.0 ms,the block and the clay are sliding along the surface as a single system.What is the force of the clay on the block during the collision?

A)450 N
B)4500 N
C)500 N
D)2250 N

Question 38

In a shuffleboard game,the puck slides a total of 12 m before coming to rest.If the coefficient of kinetic friction between the puck and board is 0.10,what was the initial speed of the puck?

A)4.8 m/s
B)48.5 m/s
C)3.8 m/s
D)4.3 m/s

Question 39

The figure shows a 100 kg block being released from rest from a height of 1.0 m.It then takes 0.90 s to reach the floor.What is the mass of the block on the left?

A)60 kg
B)54 kg
C)48 kg
D)42 kg

Question 40

A driver in a 1000.0 kg car traveling at 24 m/s slams on the brakes and skids to a stop.If the coefficient of friction between the tires and the road is 0.80,how long will the skid marks be?

A)37 m
B)30 m
C)46 m
D)34 m

Question 41

A car is being towed at constant velocity on a horizontal road using a horizontal chain.The tension in the chain must be equal to the weight of the car in order to maintain constant velocity.

Question 42

Two blocks,A and B,are being pulled to the right along a horizontal surface by a horizontal 100 N pull,as shown in the figure.Both of them are moving together at a constant velocity of 2.0 m/s to the right,and both weigh the same.Which of the figures below shows a correct free-body diagram of the horizontal forces acting on upper block,A?

A)

B)

C)

D)

E)

Question 43

In the figure,a 10 lb weight is suspended from two spring scales,each of which has negligible weight.Thus

A)each scale will read 5 lb.
B)the top scale will read zero,the lower scale will read 10 lb.
C)the lower scale will read zero,the top scale will read 10 lb.
D)each scale will show a reading between one and 10 lb,such that the sum of the two is 10 lb.However,exact readings cannot be determined without more information.
E)None of these is true.

Question 44

You are in a elevator which starts accelerating upward.Explain what happens to your apparent weight,and why.

Question 45

A stone rolls down a sloping hillside.The normal force that the surface of the hill exerts on the stone is equal to the stone's weight.

Question 46

Two unequal masses M and m are connected by a light cord passing over a pulley of negligible mass.When released,the system accelerates.Friction is negligible. Which figure below gives the correct free-body force diagrams for the two masses in the moving system?

A)

B)

C)

D)

Question 47

A rope is tied to a large crate,which is sitting on a flat surface.The coefficient of static friction between the crate and the ground is 0.9.If a person is to pull on the rope with the minimum force needed such that the crate begins to slide,the angle between the rope and the ground should be

A)greater than 0 degrees but less than 90 degrees.
B)0 degrees (rope is horizontal).
C)90 degrees.

Question 48

A 150 N box is being pulled horizontally in a wagon accelerating uniformly at 3.00 m/s2.The box does not move relative to the wagon,and the coefficient of static friction between the box and the wagon's surface is 0.600.The static friction force on this box is 90.0 N.

Question 49

A falling body accelerates downward until the drag force of the air is equal to the object's weight.After that point,the object will gradually come to rest.

Question 50

At breakfast one morning,you notice something printed on your cereal box which says
"1.0 lb = 0.454 kg." What is wrong with this information?

Question 51

Explain,from a force standpoint,how a rear spoiler on a race car helps keep the car on the road at high speeds.

Question 52

If you were to move into outer space far from any stars or planets,

A)your mass would change,but your weight would not change.
B)your weight would change,but your mass would not change.
C)both your weight and mass would change.
D)neither your weight nor your mass would change.
E)None of these is true.

Question 53

You lean against a 200 kg cabinet.The coefficient of static friction between the cabinet and floor is 0.95.Will the cabinet move? Support your answer.

Question 54

A block is at rest on a rough incline as shown. The frictional force acting on the block,along the incline,is

A)zero.
B)equal to the weight of the block.
C)greater than the weight of the block.
D)less than the weight of the block.

Question 55

A 615 N student standing on a scale in an elevator notices that the scale reads 645 N.From this information,the student knows that the elevator must be moving upward.

Question 56

If we step on the gas pedal of a car we will accelerate.Why don't we differentiate this action from braking? After all,when the brakes are applied the car decelerates,and that is different from accelerating.

Question 57

A box of mass m is pulled with a constant acceleration a along a horizontal frictionless floor by a wire that makes an angle of 15 degrees above the horizontal.The tension in this wire is greater than ma.

Question 58

A cyclist is riding up a hill having a constant slope of 30º with respect to the horizon at a constant speed (in a straight line).Which statement is true?

A)The net force on the bike (due to gravity,the normal force,and friction)is zero.
B)The net force on the bike (due to gravity,the normal force,and friction)is in the direction of motion.
C)The net force on the bike (due to gravity,the normal force,and friction)is in the opposite direction of motion.
D)None of the above statements are true.

Question 59

A brick initially has its largest-area face in contact with a rough surface,as shown on the left in the figure.A force F is required to pull the brick along the surface at constant speed. The brick is now flipped so that a face of smaller area is in contact,as on the right in the figure.The material of the brick is uniform on all faces.What force is now required to pull the brick along at constant speed as before?

A)a smaller force
B)the same force
C)a greater force
D)One cannot say without knowing the coefficient of friction.