PHYS 121 - Bank of Questions for Exam 1

Ch. 1 (

True or False: A runner completes one full lap around a track and returns to the starting point. The runner’s average speed is zero, even though the average velocity is not zero.

False

A cyclist travels 720 m in 60.0s. What is the cyclist’s average speed in m/s?

12 m/s

A car slows down uniformly form 210 m/s to 10.0 m/s in 8.0 sec.

a) What is the car’s acceleration? b) How far does the car travel during this time? Assume constant acceleration

a) -25 m/s²

b) 880 m

You fly a kite 5 ft off the ground with 300 ft of string. There is a 60 mile per hour wind, and the kite forms an angle 29° from the horizontal. How high is the kite (from the ground)?

150 ft

A 20ft ladder rests against a vertical wall and makes an angle of 65° with the ground. How high up the wall does the ladder reach?

18 ft

What must your car’s average speed be in order to travel 235 km in 2.75 hr?

23.75 m/s

A person jogs eight complete laps around a 400-m track in a total time of 14.5 min. Calculate:

a) the average speed

b) the average velocity, in m/s

a) 3.68 m/s

b) 0 m/s

Two cars approach each other on parallel raods. Each has a velocity of 155 km/hr with respect to the ground. I

a) f they are initially 8.5 km apart, how long will it take before they reach each other?

b) How far does each car travel before they reach each other?

a) t = 0.0274

b) 4.25 km & 4.25 km

A car accelerates from 14 m/s to 21 m/s in 6.0 s. a) What was its acceleration? b) How far did it travel in that time? Assume constant acceleration

a) 1.17 m/s²

b) 105.06 m

A car slows down uniformly from a speed of 28.0 m/s to rest in 8.00 s. How far did it travel in that time?

112 m

A space vehicle accelerates uniformly from 85 m/s at t = 0 to 162 m/s at t = 10s. How far did it move between t = 2.0 sec and t = 6.0 sec.

463.2 m

You drop a rock off a bridge. When the rock has fallen 4 m, you drop a second rock. As the two rocks continue to fall, what happens to their velocities?

Both increase at the same rate

You throw a rock straight upward. As the rock rises, what happens to its speed? Ignore Air Resistance

It decreases at a constant rate

A falling stone takes 0.36 sec to travel past a window that is 2.4 m tall.

a) From what heigh above the top of the window was the stone dropped?

b) What is the stone’s velocity when it reaches the bottom edge of the window? State both the magnitude and the direction of the velocity.

a) -4.9 m/s

b) -8.428 m/s, downwards

True or False: Projectile Motion is Linear

FALSE, Projectile motion is parabolic

There are two vectors. Vector A is directed east and Vector B is directed North. The magnitudes of Vector A and Vector B are 40 and 25 units, respectively. Determine the magnitude and angle of A - B. Show all works.

Magnitude: 31.2

Angle: -32.0°

A hunter is 42 m away from a target (on the same level) and aims direectly at his target. The arrow leaves the bow at 20.3 m/s. Ignore air resistance.

a) If the hunter aims horizontally at the target, by how much will the arrow miss the target? Give magnitude and direction

b) To hit the target, the arrow takes 3.00sec to reach it. At what angle should the hunter shoot?

a) -20.9 m, downward

b) 46.4°

An automobile traveling 95 km/hr overtakes a 1.30 km long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h, a) how long does it take the car to pass it, and b) how far will the car have traveled in that time?

a) t = 0.065 hr

b) 6.18 km

A stone is dropped from the top of a cliff. It is seen to hit the ground below after 3.55 sec. How high is the cliff?

61.75 m

An unmarked police car traveling a constant 95 km/hr is passed by a speeder traveling 135 km/h. Precisely 1.00sec after the speeder passes, the police officer steps on the accelerator; if the police car’s acceleration is 2.60 m/s², how omuch time passes before the police car overtakes the speeder (assumed moving at constant speed?

10.45 sec

A baseball is seen to pass upward by a window with a vertical speed of 14 m/s. If the ball was thrown by a person 18m below on the street, a) what was its initial speed, b) what altitude did it reach, c) when was it thrown and d) when does it reach the street again?

a) 23.42 m/s

b) 28 m

c) 0.96 sec

d) 4.78 sec

If V_x = 9.80 units and V_y= -6.40 units.

a) Determine the magnitude and direction of Vector V.

b) Rewrite this using proper unit vector notation

a) 11.70 units, -33.1° (4th Quadrant) OR 326.9°

B) 9.80 î, 6.40 ĵ

On mountainous downhill roads, escape routes are sometimes placed to the side of the raod for trucks whose brakes might fail. Assuming a constant upward slope of 26°, calculate the horizontal and vertical components of the acceleration of a truck that slowed from 110 km/h to rest in 7.0s.

-3.92 m/s², -1.91 m/s²

An airplane is traveling 835 km/hr in a direction 41.5° west of north. Find the components of the velocity vector in the northern and western directions. How far north and how far west has the plane traveled after 17.5 hr?

North: 10937 km

West: 9677 km

A football is kicked at ground level with a speed of 18.0 m/s at an angle of 31° to the horizontal.

a) What are the components of the initial velocity?

b) How long does it take to reach the peak?

c) What is the maximum height?

d) What is the maximum horizontal displacement?

A) Vx₀=15.43 m/s, Vy₀=9.27 m/s

B) 0.945 sec

C) 4.38 m

d) 1.84 sec

You are running along the rooftop and need to jump off. You decide to leap off horizontally with a speed of 3.0 m/s and free fall to land on a small platform below. The platform is 14m form the base of the building you leaped off of. a) Determine how high the building needs to be to successfully land on the platform and b) what velocity (magnitude and direction) you land with.

a) -106.8 km

b) -4.76 m/s, 96.25° horizontally

A projectile is launched form the top of a 20.0 m high building with an initial speed of 25.0 m/s at an angle of 35.0° above the horizontal. Neglect air resistance. a) How long is the projectile in the air before it reaches the ground? b) How far horizontally from the base of the building does it land? c) Find the magnitude and direction of its velocity just before it hits the ground.

a) 3.96 sec

b) 81.1 m

c) 31.9 m/s, 50°

A train moves eat at 18.0 m/s relative to the ground. A student walks inside the train at 2.50 m/s relative to the train.

a) Find the student’s velocity relative to the ground when the student walks toward the front of the train (east).

b) Find the student’s velocity relative to the ground when the student walks towards the rear of the rain (west) at the same speed. State the direction in each case.

a) 20.5 m/s east/forward

b) 15.5 m/s east/forward

A river current flows west at 4.00 m/s relative to the shore. A boat can travel at 13.0 m/s relative to the water. The pilot wants the boat to move straight north across the river. a) At what angle east of north should the boat be pointed relative to the water? b) What is the boat’s speed relative to the shore? c) If the river is 180 m wide, how long will it take the boat to cross?

a) 17.92° east of north

b) 12.37 m/s

c) 14.55 sec

A box of mass 25.0 kg rests on a horizontal floor. What is the normal force exerted by the floor on the box?

245 N, upward

A car of mass 1400 kg traveling at 27.0 m/s is brought to rest uniformly over a distance of 62.0 m on a level road. Ignore air resistance.

a) Determine the car’s acceleration and stopping time.
b) Determine the net horizontal force exerted by the road on the car while it is stopping.

c) Determine the magnitude and direction of the force the car exerts on the road during the stop. Clearly identify the action-reaction pair.

a) -5.88 m/s

b) -8.23×10³ N

c) 1.60×10⁴, -59.0° (4th Quad)

A 14.0kg bucket is lowered vertically by a rope in which there is 163N of tension at a given instant. What is the acceleration of the bucket? Is it up or down?

1.84 m/s² up

A 10.0 kg box slides along a horizontal floor. The coefficient of kinetic friction is 0.20. What is the magnitude of the frictional force acting on the box?

19.6 N

Two crates, of mass 65 kg and 125 kg, are in contact and at rest on a horizontal surface. A 650 N force is exerted on the 65 kg crate. If the coefficient of kinetic friction is 0.18, calculate

a) the acceleration of the system

b) The force that each crate exerts on the other

c) Repeat with the crates reversed

a) 1.66 m/s²

b) 427.44 N

c) 222N

The following figure shows a block (mass mA) on a smooth horizontal surface, connected by a thin cord which passes over a pulley to a second block (mass mB), which hangs vertically.

a) Draw a free body diagram for each block

b) Apply Newton’s second law to find formulas for the acceleration of the system and for the tension in the cord (ignore friction and the mass of the pulley and the cord)

c) if mA = 13.0 kg and mB = 5.0 kg determine the acceleration of each block.

d) If initially mA is at rest 1.250 m from the edge of the table, how long does it take to reach the edge of the table if the system is allowed to move freely?

e) if mB = 1.0 kg, how large must mA be if the acceleration of the system is to be kept at 1/100g?

a) image

b) T = mAmBg/mA + mB & a = mBg/mA + mB

c) 2.72 m/s²

d) 0.958 sec

e) mA = 99 kg

How many SI base units will be presented within both semesters of this physics course?

7

Acceleration is to Velocity as Velocity is to

Displacement

Express the number 0.02 days using the correct prefix

2 centidays

What is the percent uncertainty in the measurement 2.58 ± 0.15 cm?

5.8%

The number of significant figures in 0.01500 is:

Four

Which statement is false about a projectile at the top of its trajectory (pathway)?

Its acceleration is zero

You throw a ball straight up in the air. After it leaves your hand, at what point in its flight does the ball undergo its maximum value of acceleration

It acceleration is constant everywhere

Object A and B start at rest. They then both accelerate at the same rate. However, object A accelerates for twice the amount of time as object B does. What is the final speed of object A compared to object B?

Twice as fast

If two vectors have a magnitude of 3 and 5, which value is impossible as the resultant of these two vectors?

9

Rufus can only swim at one speed: fast. He swims fast straight across a river on a day when there is no current in the river. It takes him only 5 minutes to get to the other side. If he repeats this the next day, aiming straight across, but the river has a current this time, which statement is true?

Rufus crosses in the same amount of time but lands further downstream

A heavier large stone sits upon a smaller lighter stone, which sits on the ground. Compared to the force of the heavier stone upon the lighter one, the force of the lighter stone upon the heavier one is:

Same

A stone of mass M sits upon a scale, which sits at rest upon an incline making angle θ with the ground. The reading of the scale is:

mg Cosθ, equal of the normal force, less than the weight

What is Newton’s 3rd law of Motion?

Whenever one object exerts a force on a second object, the second exerts an equal force in the opposite direction on the first. (For every action, there is an equal and opposite reaction.)

What is Newton’s 1st Law of Motion?

Every object continues in its state of rest, or of uniform velocity in a straight line, as long as no net force acts on it. (An object at rest stays at rest, and an object in motion stays in motion at a constant speed in a straight line, unless an outside force acts on it)

What is Newton’s 2nd Law of Motion?

The force on an object is equal to its mass multiplied by its acceleration (F = ma)

Upon a train moving at 20. m/s relative to the ground, you walk forward (in the direction the train moves) at 3.0 m/s relative to the train, while rolling a ball backward along your extended arm at 1.0 m/s relative to you. The velocity of the ball relative to the ground is:

22 m/s forward

How many basic units does the SI system have?

Seven

The base SI unit of time is which of the following?

The second

The correct conversion factor between km/h and m/s is:

0.278 m/s

When the rocket engines accelerating starship Sufur are suddenly turned off, while traveling in empty space, the starship will:

Move with constant speed

You are standing in a moving bus, facing forward and you suddenly fall forward from the bus’s motion. You can imply from this that the bus:

Decreased Velocity