Exam 2: Motion in One Dimension

A car with good tires on a dry road can decelerate (slow down) at a steady rate of about 5.0 m/s² when braking. If a car is initially traveling at 55 mi/h (a) how much time does it take the car to stop? (b) what is its stopping distance?

Assuming equal rates of acceleration in both cases, how much longer would it take a car to stop if braking from 56 mi/h than from 28 mi/h?

Two cars are traveling at the same speed and hit the brakes at the same time. Car A decelerates (decreases its velocity) at twice the rate of car B. If car B takes time T to stop, how long does it take car A to stop?

A polar bear starts at the North Pole. It travels 1.0 km south, then 1.0 km east, and then 1.0 km north to return to its starting point. This trip takes 45 min. What was the bear's average velocity?

If the position versus time graph of an object is a horizontal line, the object is

A 10-kg rock and 20-kg rock are dropped from the same height and experience no significant air resistance. If it takes the 20-kg rock a time T to reach the ground, what time will it take the 10-kg rock to reach the ground?

You drive 6.0 km at 50 km/h and then another 6.0 km at 90 km/h. Your average speed over the 12 km drive will be

An airplane travels at 300 mi/h south for 2.00 h and then at 250 mi/h north for 750 miles. What is the average speed for the trip?

Which of the following quantities has units of a velocity? (There could be more than one correct choice.)

From the edge of a roof top you toss a green ball upwards with initial speed v₀ and a blue ball downwards with the same initial speed. Air resistance is negligible. When they reach the ground below

A 10-kg rock and a 20-kg rock are thrown upward with the same initial speed v₀ and experience no significant air resistance. If the 10-kg rock reaches a maximum height h, what maximum height will the 20-kg ball reach?

You leave on a 549 - $\text{mi}$ trip in order to attend a meeting that will start $10.8 \mathrm {~h}$ after you begin your trip. Along the way you plan to stop for dinner. If the fastest you can safely drive is 65 mi/h, what is the longest time you can spend over dinner and still arrive just in time for the meeting?

In a ballistics test, a bullet moving horizontally with a speed of 500 m/s strikes a sandbag and penetrates a distance of 10.0 cm. (a) What is the magnitude of the average acceleration of the bullet in the sandbag? (b) How many milliseconds does it take the bullet to come to rest in the sandbag?

An airplane increases its speed at the average rate of 15 m/s². How much time does it take to increase its speed from 100 m/s to 160 m/s?

A racquetball strikes a wall with a speed of 30 m/s and rebounds in the opposite direction with a speed of 26 m/s. The collision takes 20 ms. What is the average acceleration of the ball during the collision with the wall?

Suppose a ball is thrown straight up and experiences no appreciable air resistance. What is its acceleration just before it reaches its highest point?

Human reaction times are worsened by alcohol. How much further (in feet) would a drunk driver's car travel before he hits the brakes than a sober driver's car? Assume that both are initially traveling at 50.0 mi/h and their cars have the same acceleration while slowing down, and that the sober driver takes 0.33 s to hit the brakes in a crisis, while the drunk driver takes 1.0 s to do so. (5280 ft = 1 mi)

The figure shows a graph of the position of a moving object as a function of time. (a) What is the average velocity of the object from t = 0 s to t = 4.0 s? (b) What is the average velocity of the object from t = 0 s to t = 6.0 s?

Consider a deer that runs from point A to point B. The distance the deer runs can be greater than the magnitude of its displacement, but the magnitude of the displacement can never be greater than the distance it runs.

A ball is thrown downward in the absence of air resistance. After it has been released, which statement(s) concerning its acceleration is correct? (There could be more than one correct choice.)