AP Physics HW Check 1

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

112m

A ball player catches a ball 3.4 s after throwing it vertically upward. With what speed did he throw it and what height did it reach?

17m/s; 14m

A kangaroo jumps straight up to a vertical height of 1.45 m. How long was it in the air before returning to Earth?

1.09 s

Two locomotive approach each other on parallel tracks. Each has a speed of 155 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other?

1.6 min

A car traveling 95 km/h is 210 m behind a truck traveling 75 km/h. How long will it take the car to reach the truck?

38 s

A car traveling at 95 km/h strikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.80 m. What was the magnitude of the average acceleration of the driver during the collision? Express the answer in terms of gs where 1.00g=9.80m/s²

44g

A helicopter is ascending vertically with a speed of 5.40m/s. At a height of 105 m above the Earth, a package is dropped from the helicopter. How much time does it take for the package to reach the ground?

5.21 s

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

61.8m

Does a car speedometer measure speed, velocity, or both? Explain.

A car speedometer measures speed, which is how quickly an object moves. It doesn't provide information on which direction the car is moving, so it doesn't measure velocity.

Which of these motions is NOT at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, and a dish resting on a table? Explain your answers.

An elevator moving from the second to fifth floor making stops along the way isn't at constant acceleration because the acceleration would change in direction and the velocity would change at an inconsistent rate as it stops and starts. A rock falling from a cliff has constant acceleration because of gravity pulling downward if air resistance is ignored. A dish resting on a table is at a constant acceleration of zero.

Give an example where both the velocity and acceleration are negative.

If an object moves in a negative direction, like if you drop a ball from a ladder, then it speeds up in that direction, as the velocity gets more negative in the negative direction, the change in velocity is negative. Therefore, it has both a negative velocity and negative acceleration.

If one object has a greater speed than a second object, does the first necessarily have a greater acceleration? Explain, using examples.

No because a faster object could travel at a constant speed of 8m/s in a positive direction the whole time, which makes it acceleration zero because there's no change in its average velocity. However, an object traveling at a slower speed could change its speed from 2 m/s to 4 m/s, which makes its acceleration greater than zero, as it causes a positive change in average velocity. Ex: a bicyclist rides at a constant speed and another slower bicyclist speeds up

When an object moves with constant velocity, does its average velocity during any time interval differ from its instantaneous velocity at any instant? Explain.

No because if an object moves with constant velocity, its position changes at a constant rate in the same direction, so its average velocity is constant. Its average velocity would be the same at any given instant in time.

Describe in words the motion plotted in the figure in terms of velocity, acceleration etc. (position vs time curve)

Slope of position vs time curve is velocity. The object starts at 0 and changes position at constant rate from 0 to 20 seconds, so it has constant velocity that's positive and zero acceleration. From 20 to 30 seconds, object changes position at faster rate, so it speeds up in a positive direction with positive acceleration (positive curve) and increased velocity. From 30 to 45 seconds, the object slows down until it stops when it has zero velocity as there's no change in position and then changes direction. It moves in a negative direction (negative curve) and speeds up in that direction. From 45-50 seconds, objects slows down in negative direction, so it has positive acceleration (positive curve)

Describe the words in motion of the object graphed in the figure (velocity vs time curve)

Slope of velocity vs time curve is acceleration. From 0 to 40 seconds, object starts at positive velocity and speeds up with constant acceleration until velocity of +37m/s. Then acceleration decreases to 0 around 50 seconds as the maximum velocity is about 39m/s. the object's velocity decreases as it slows down. At 90 seconds, object comes to rest until about 106 seconds, when it increases its velocity as faster rate in positive direction with positive large acceleration and then smaller acceleration

Compare the acceleration of a motorcycle that accelerates from 80 km/h to 90 km/h with the acceleration of a bicycle that accelerates from rest to 10km/h in the same time.

The acceleration of the motorcycle is the same as that of the bicycle, as the change of velocity of the motorcycle is 90km/h-80km/h=10km/h and that of the bicycle is 10km/h-0km/h=10km/h. Since they have the same change in velocity in the same amount of time, they have the same acceleration.

Determine the stopping distances for an automobile going a constant initial speed of 95 km/h and human reaction time of 0.40 s: a) for an acceleration a=-3.0 m/s² b) for a= -6.0 m/s²

a) 130m b) 69m

Can an object have a northward velocity and a southward acceleration? Explain.

Yes because an object can be traveling northward in a positive direction and therefore have a northward velocity, but then slow down, which changes its velocity, as it becomes less positive. This would make the final velocity less than the initial velocity, making the change in velocity negative and the acceleration southward.

Can an object have zero acceleration and nonzero velocity at the same time? Give examples

Yes because an object traveling at a constant nonzero velocity has zero acceleration because there is no change in velocity. For example, a car moving at a constant speed in a straight line.

Can an object be increasing in speed as its acceleration decreases? If so, give an example. If not, explain.

Yes because if an object increases its speed from 5 m/s to 10 m/s in 1 second and then from 10m/s to 13 m/s 1 second after in the same direction, its acceleration in the second time interval is less than that in the first time interval. Therefore, its acceleration decreases as its speed increases. Velocity can increase as its rate of increase decreases. Ex: a car starts at rest then presses on the gas and then speeds up less than before

Can the velocity of an object be negative when its acceleration is positive? What about vice versa? If yes, give an example in each case.

Yes because the negative velocity means that the object moves in a negative direction, but then slows down, as the velocity gets less negative, which makes the change in velocity positive and the acceleration positive. On the other hand, if the object moves in a positive direction, it has a positive velocity. If it slows down, the velocity becomes less positive. The change in velocity becomes negative, making the acceleration negative. Ex: if a car moves to the left (negative direction) and slows or if it moves to the right and slows

Can an object have zero velocity and nonzero acceleration at the same time? Give examples

Yes. For example, a ball thrown straight up has a constant nonzero downward acceleration because of gravity on the way up, but at the highest point, it momentarily stops for an instant because the downward acceleration/force of gravity causes it to slow and then stop, at which point the velocity is zero.

you drop rock off bridge. When rock has fallen 4m, you drop 2nd rock. As 2 rocks continue to fall, what happens to their velocities? a. both increase at same rate b. velocity of 1st rock increases faster than velocity of 2nd c. velocity of 2nd rock increases faster than velocity of 1st d. both velocities stay constant

a

position of rabbit along straight tunnel as function of time is plotted in figure. What's its instantaneous velocity a) at t=10.0s and b) t=30.0s. What's its average velocity c) between t=0 and t=5.0s, d) between t=25.0s and t=30.0s, and e) between t=40.0s and t=50.0s?

a. 0.3m/s b. 1.2m/s ?c. 0.30/ms ?d. 1.4m/s ?e. -0.95m/s

A person jogs 8 complete laps around a 400-m track in a total time of 14.5 min. Calculate a) its average speed and b) its average velocity for the entire trip, using "away from the trainer" as the positive direction.

a. 3.68 m/s b. 0

You are driving home from school steadily at 95 km/h for 180 km. It then begins to rain and you slow to 65 km/h. You arrive home after driving 4.5h. a)How far is your hometown from school? b) What was your average speed?

a. 350 km b. 78 km/h draw diagram

stone thrown vertically upward with speed of 15.5m/s from edge of cliff 75.0m high. a) how much later does it reach bottom of cliff? b) what is its speed just before hitting? c) what total distance did it travel?

a. 5.80s b. 41.4 m/s c. 99.5 m

car travels along x axis with increasing speed. We don't know if to the left or right. Which of graphs in figure most closely represents motion of car?

a; because slope of position vs time curve is velocity; increasing speed means slope gets larger in magnitude

Which of the following should be part of solving any problem in physics? Select all: a. Read problem carefully b. Draw picture of situation c. write down variables given d. think about which physics principles to apply e. determine which equations can be used to apply correct physics principles f. check units when you've completed your calculation g. consider whether your answer is reasonable

all of them

ball thrown downward at speed of 20m/s. Choosing +y axis pointing up and neglecting air resistance, which equation/s could be used to solve for other variables? The acceleration due to gravity if 9.8m/s² downward: a. v=(20m/s)-gt b. y=y₀+(-20m/s)t-(1/2)gt² c. v²=(20m/s)²-2g(y-y₀) d. 20m/s=(v+v₀)/2 e. all of the above

b, c

ball dropped from top of tall building. At same instant, 2nd ball is thrown upward from ground level. When 2 balls pass one another, one on way up and other on way down, compare magnitudes of their acceleration: a. acceleration of ball dropped is greater b. acceleration of ball thrown upward is greater c. acceleration of both balls is same d. acceleration changes during motion, so you can't predict exact value when 2 ball pass each other e. accelerations are in opposite directions

c

ball is thrown straight up. What are velocity and acceleration of ball at highest point in its path? a. v=0, a=0 b. v=0, a=9.8m/s² up c. v=0, a=9.8m/s² down d=9.8 m/s up, a=0 e. v=9.8m/s down, a=0

c

you drive 4km at 30km/h and then another 4km at 50km/h. What's your average speed for whole 8km trip? a. more than 40km/h b. equal to 40km/h c. less than 40km/h d. not enough information

c

at time t=0 object travels to the right along +x axis at speed of 10.0m/s with acceleration -2.0m/s². Which is true? a. object will slow down eventually coming to complete stop b. object can't have negative acceleration and be moving to right c. object will continue to move to right, slowing down but never coming to complete stop d. object will slow down, momentarily stopping, then pick up speed moving to left

d

in which of the following cases does a car have negative velocity and positive acceleration? A car that is traveling in the: a. -x direction at constant 20m/s b. -x direction increasing in speed c. +x direction increasing in speed d. -x direction decreasing in speed e. +x direction decreasing in speed

d

velocity (magnitude and direction) with vectors includes

magnitude and angle with respect to horizontal axis