Physics Lecture 3

A ball is projected upward at time t = 0.0 s, from a point on a roof 90 m above the ground. The ball rises, then falls and strikes the ground. The initial velocity of the ball is 80.5 m/s. Consider all quantities as positive in the upward direction. The velocity of the ball when it is 89 m above the ground is closest to: A) - 81 m/s B) - 64 m/s C) - 48 m/s D) - 32 m/s E) - 97 m/s

A

A bicyclist starts a timed race at 6.0 mi/h. In order to win, he must average 21 mi/h. Assuming constant acceleration from the start, how fast must he be traveling at the end of the race? A) 36 mi/h B) 30 mi/h C) 24 mi/h D) 42 mi/h

A

A dragster travels 1/4 mi in 6.7 s. assuming that acceleration is constant and the dragster is initially at rest, what is its velocity when it crosses the finish line? A) 269 mi/h B) 188 mi/h C) 296 mi/h D) 135 mi/h

A

A package is dropped from a helicopter moving upward at 15 m/s. If it takes 16.0 s before the package strikes the ground, how high above the ground was the package when it was released? (Disregard air resistance.) A) 1000 m B) 1500 m C) 810 m D) 1200 m

A

A sports car can go from rest to 32 m/s in 3.88 s. The same car can come to a full stop from that speed in 3.96 s. What is the ratio of starting to stopping accelerations? A) -1.0 B) 1.0 C) -0.98 D) 0.98

A

A toy rocket is launched vertically from ground level (y = 0 m), at time t = 0.0 s. The rocket engine provides constant upward acceleration during the burn phase. At the instant of engine burnout, the rocket has risen to 49 m and acquired a velocity of 60 m/s. The rocket continues to rise in unpowered flight, reaches maximum height, and falls back to the ground. The maximum height reached by the rocket is closest to: A) 233 m B) 221 m C) 209 m D) 244 m E) 256 m

A

A ball is thrown straight upward with a velocity of 39 m/s. How much time passes before the ball strikes the ground? (Disregard air resistance.) A) 4.0 s B) 8.0 s C) 2.4 s D) 1.2 s

B

At the same moment, one rock is dropped and one is thrown downward with an initial velocity of 10 m/s from the top of a 300 m building. How much earlier does the thrown rock strike the ground? (Disregard air resistance.) A) 0.65 s B) 0.95 s C) 0.85 s D) They land at exactly the same time

B

A car moving at a velocity of 20 m/s is behind a truck moving at a constant velocity of 18 m/s. When the car is 50 m behind the front of the truck, the car accelerates uniformly at 1.8 m/s2. The car continues at the same acceleration until it reaches a velocity of 25 m/s, which is the legal speed limit. The car then continues at a constant velocity of 25 m/s, until it passes the front of the truck. The distance the car travels while accelerating, in meters, is closest to: A) 50 B) 54 C) 58 D) 62 E) 66

D

A test rocket is fired straight up from rest with a net acceleration of 20 m/s2. After 4 seconds the motor turns off, but the rocket continues to coast upward. What maximum elevation does the rocket reach? A) 408 m B) 327 m C) 320 m D) 487 m E) 160 m

D

A toy rocket is launched vertically from ground level (y = 0 m), at time t = 0.0 s. The rocket engine provides constant upward acceleration during the burn phase. At the instant of engine burnout, the rocket has risen to 81 m and acquired a velocity of 40 m/s. The rocket continues to rise in unpowered flight, reaches maximum height, and falls back to the ground. The upward acceleration of the rocket during the burn phase is closest to: A) 9.0 m/s2 B) 9.6 m/s2 C) 9.3 m/s2 D) 9.9 m/s2 E) 8.7 m/s2

D

A train starts from rest and accelerates uniformly, until it has traveled 5.6 km and acquired a velocity of 42 m/s. The train then moves at a constant velocity of 42 m/s for 420 s. The train then slows down uniformly at 0.065 m/s2, until it is brought to a halt. The acceleration during the first 5.6 km of travel is closest to: A) 0.19 m/s2 B) 0.14 m/s2 C) 0.17 m/s2 D) 0.16 m/s2 E) 0.20 m/s2

D

An airplane needs to reach a velocity of 203.0 km/h to take off. On a 2000 m runway, what is the minimum acceleration necessary for the plane to take flight? A) 1.0 m/s2 B) 0.87 m/s2 C) 0.95 m/s2 D) 0.79 m/s2

D

A ball is projected upward at time t = 0.0 s, from a point on a roof 60 m above the ground. The ball rises, then falls and strikes the ground. The initial velocity of the ball is 28.4 m/s. Consider all quantities as positive in the upward direction. At time t = 4.3 s, the acceleration of the ball is closest to: A) zero B) +5 m/s2 C) +10 m/s2 D) -5 m/s2 E) -10 m/s2

E

If an object stops moving at a point, then its acceleration must be zero at that point.

F

It is physically impossible for an object to have a negative acceleration and yet be speeding up

F

Negative acceleration is called deceleration because an object is slowing down.

F

The equation sf = si + vis Δt +1/2 as (Δt)2 is valid for all types of motion because it is a fundamental equation of physics.

F

If the "velocity versus time" graph of an object is a horizontal line, that object cannot be accelerating.

T

The acceleration is always the slope of the "velocity versus time" graph and the velocity is always the slope of the "position versus time" graph.

T

The equation vfs2 = vis2+ 2as Δx applies to motion for which the "velocity versus time" graph is a straight line.

T

A toy rocket is launched vertically from ground level (y = 0 m), at time t = 0.0 s. The rocket engine provides constant upward acceleration during the burn phase. At the instant of engine burnout, the rocket has risen to 64 m and acquired a velocity of 60 m/s. The rocket continues to rise in unpowered flight, reaches maximum height, and falls back to the ground. The time interval, during which the rocket engine provides upward acceleration, is closest to: A) 2.1 s B) 2.3 s C) 1.9 s D) 1.7 s E) 1.5 s

A

A train starts from rest and accelerates uniformly, until it has traveled 2.1 km and acquired a velocity of 24 m/s. The train then moves at a constant velocity of 24 m/s for 400 s. The train then slows down uniformly at 0.065 m/s2, until it is brought to a halt. The distance traveled by the train while slowing down, in km, is closest to: A) 4.4 B) 4.2 C) 4.0 D) 3.8 E) 3.6

A

The average velocity of a car over a certain time interval is 37 mi/h. If the velocity of the car was 65 mi/h at the end of this interval, what was its initial velocity? Assume that acceleration was constant. A) 9 mi/h B) 13 mi/h C) 4.0 mi/h D) 57 mi/h

A

A car accelerates from 5.0 m/s to 21 m/s at a rate of 3.0 m/s2. How far does it travel while accelerating? A) 41 m B) 207 m C) 69 m D) 117 m

C

A car is travelling north at 17.7 m/s. After 12 s its velocity is 14.1 m/s in the same direction. Find the magnitude and direction of the car's average acceleration. A) 0.30 m/s2, North B) 2.7 m/s2, South C) 0.30 m/s2, South D) 2.7 m/s2, North

C

A racquetball strikes a wall with a speed of 30 m/s and rebounds with a speed of 26 m/s. The collision takes 20 ms. What is the average acceleration of the ball during the collision? A) zero B) 200 m/s2 C) 2800 m/s2 D) 1500 m/s2

C

Assuming equal rates of acceleration in both cases, how much further would you travel if braking from 56 mi/h to rest than from 28 mi/h? A) 4.8 times farther B) 3.2 times farther C) 4 times farther D) 5.2 times farther

C