1.
A car goes from 30 miles per hour (mph) to 60 mph in six seconds. The acceleration of the car is:
Correct Answer
A. 5 mph per second.
Explanation
The acceleration of the car can be calculated by dividing the change in velocity by the time taken. In this case, the change in velocity is 60 mph - 30 mph = 30 mph. The time taken is 6 seconds. Therefore, the acceleration is 30 mph / 6 seconds = 5 mph per second.
2.
The graph below represents the speed of a car vs. time.
Figure 4-1
Which point on the speed versus time graph in Figure 4-1 has the highest acceleration?
Correct Answer
B. B
Explanation
Point B on the speed versus time graph in Figure 4-1 has the highest acceleration. This can be determined by looking at the steepness of the graph at each point. Point B has the steepest slope, indicating a higher rate of change in speed over time compared to the other points. Therefore, it has the highest acceleration.
3.
A rocket has an acceleration of 50 m/sec2. How long does it take the rocket to reach a speed of 1,000 m/sec?
Correct Answer
B. 20 seconds
Explanation
The rocket has an acceleration of 50 m/sec2, which means its speed increases by 50 m/sec every second. To reach a speed of 1,000 m/sec, the rocket would need to increase its speed by 950 m/sec (1,000 - 50) from its initial speed of 50 m/sec. Since the speed increases by 50 m/sec every second, it would take 950/50 = 19 seconds to reach a speed of 1,000 m/sec. Therefore, the correct answer is 20 seconds.
4.
A sports car reaches a speed of 50 m/sec in 12 seconds after starting from rest. The acceleration of the car is:
Correct Answer
B. 4.17 m/sec^2
Explanation
The acceleration of the car can be calculated using the formula: acceleration = change in velocity / time. In this case, the change in velocity is 50 m/sec (final velocity) - 0 m/sec (initial velocity) = 50 m/sec. The time taken is 12 seconds. Therefore, the acceleration is 50 m/sec / 12 sec = 4.17 m/sec^2.
5.
The graph below represents the motion of an object.
Figure 4-2
Between two and three seconds, the speed of the object shown in Figure 4-2:
Correct Answer
C. Increases from 1 m/sec to 4 m/sec
6.
Which of the following statements CANNOT ever be true?
Correct Answer
C. An object can have a speed that is changing and still have zero acceleration.
Explanation
An object can have a speed that is changing and still have zero acceleration. This statement contradicts the definition of acceleration, which is the rate of change of velocity. If an object's speed is changing, it means its velocity is changing, and therefore it must have a non-zero acceleration.
7.
In the equation , the variable x0 represents:
Correct Answer
A. The position at time t = 0.
Explanation
The variable x0 represents the position at time t = 0. This means that it represents the initial position or the position of an object at the start of its motion. It does not represent the distance moved in the first second of motion, the speed at time t = 0, or the position when the speed equals zero.
8.
The graph below represents the motion of a moving object.
Figure 4-3
The initial speed (v0) shown in Figure 4-3 is:
Correct Answer
B. 0.2 m/sec.
9.
A car is traveling at 30 m/sec in a straight line. The driver applies the brakes for 3 seconds, and the car slows down to 12 m/sec. The acceleration of the car is:
Correct Answer
C. -6 m/sec^2
Explanation
The acceleration of the car can be calculated using the formula: acceleration = (final velocity - initial velocity) / time. In this case, the initial velocity is 30 m/sec, the final velocity is 12 m/sec, and the time is 3 seconds. Plugging these values into the formula, we get: acceleration = (12 m/sec - 30 m/sec) / 3 sec = -18 m/sec / 3 sec = -6 m/sec^2. Therefore, the acceleration of the car is -6 m/sec^2.
10.
If the speed is constant, which variable is zero in the equation ?
Correct Answer
C. A
Explanation
In the equation, if the speed is constant, it means that there is no acceleration (a). When there is no acceleration, it implies that the variable for acceleration is zero.
11.
An object falls for 2 seconds after being dropped from rest. Its speed is approximately:
Correct Answer
D. 19.6 m/sec
Explanation
When an object falls due to gravity, its speed increases at a constant rate of 9.8 m/s². This means that every second, the object's speed increases by 9.8 m/s. Since the object falls for 2 seconds, its speed would have increased by 9.8 m/s for each of those 2 seconds. Therefore, the object's speed would be approximately 19.6 m/s after falling for 2 seconds.
12.
A object is thrown straight upwards with a speed of 19.6 m/sec. Three seconds later, its speed is:
Correct Answer
B. 9.8 m/sec downward
Explanation
When an object is thrown straight upwards, its velocity decreases due to the force of gravity acting against its motion. After three seconds, the object reaches its highest point and starts to fall back down. At this point, its velocity is equal to the acceleration due to gravity, which is approximately 9.8 m/sec downward. This means that the object is moving downward at a speed of 9.8 m/sec after three seconds.
13.
The acceleration of gravity on the moon is about 1.6 m/sec2. A 2-kilogram object on the moon is dropped from rest. After ten seconds, the speed of the object is:
Correct Answer
C. 16 m/sec
Explanation
The acceleration of gravity on the moon is 1.6 m/sec2. When an object is dropped from rest, it experiences a constant acceleration due to gravity. Using the equation v = u + at, where v is the final velocity, u is the initial velocity (which is 0 m/sec since it is dropped from rest), a is the acceleration, and t is the time, we can calculate the final velocity. Plugging in the values, v = 0 + (1.6 m/sec2)(10 sec) = 16 m/sec. Therefore, after ten seconds, the speed of the object is 16 m/sec.
14.
In physics, the term free fall means:
Correct Answer
A. No forces act on the object except gravity.
Explanation
Free fall in physics refers to the motion of an object under the influence of gravity alone, without any other forces acting on it. This means that there is no air resistance or any other external force affecting the object's motion. The object will only experience the force of gravity, causing it to accelerate towards the ground. Therefore, the correct answer is "no forces act on the object except gravity."
15.
The acceleration of gravity on the moon is about 1.6 m/sec2. An experiment to test gravity compares the time it takes objects to reach a speed of 10 m/sec after being dropped from rest. How long does an object dropped on the moon have to fall compared to an object dropped on Earth?
Correct Answer
C. 9.8 times as long
Explanation
An object dropped on the moon takes 9.8 times as long to fall compared to an object dropped on Earth because the acceleration of gravity on the moon is about 1.6 m/sec2, while the acceleration of gravity on Earth is about 9.8 m/sec2. Since gravity affects the rate at which objects fall, the lower acceleration of gravity on the moon causes objects to fall more slowly, resulting in a longer time for them to reach a speed of 10 m/sec.
16.
The acceleration of gravity expressed in English units is:
a. 9.8 ft/min2.
b. 32.2 ft/sec2.
c. 9.8 ft/sec2.
d. 3.0 ft/sec2.
Correct Answer
B. 32.2 ft/sec^2
Explanation
The correct answer is b. 32.2 ft/sec2. This is the correct answer because the acceleration of gravity is commonly expressed as 32.2 ft/sec2 in English units. This value represents the rate at which an object falls due to gravity in feet per second squared.
17.
A clever person who knows physics measures the depth of a deep hole by dropping a rock into the hole. The rock takes 3.2 seconds to hit the bottom. The depth of the hole is approximately:
Correct Answer
C. 50 meters
Explanation
The time it takes for an object to fall freely under the influence of gravity can be calculated using the equation t = √(2h/g), where t is the time, h is the height, and g is the acceleration due to gravity. In this case, the rock takes 3.2 seconds to hit the bottom, so we can rearrange the equation to solve for h: h = (g * t^2) / 2. Assuming the acceleration due to gravity is approximately 9.8 m/s^2, plugging in the values gives us h = (9.8 * 3.2^2) / 2 = 50.24 meters. Since we are asked for an approximate value, the depth of the hole is approximately 50 meters.
18.
An arrow is shot straight up into the air at a speed of 98 m/sec. What is the maximum height reached by the arrow? You may neglect air friction.
Correct Answer
B. 490 meters
Explanation
The maximum height reached by the arrow can be determined using the equation for vertical motion under constant acceleration. The initial velocity of the arrow is 98 m/sec and the acceleration due to gravity is -9.8 m/s^2 (negative because it acts in the opposite direction to the motion). Using the equation v^2 = u^2 + 2as, where v is the final velocity (0 m/s at maximum height), u is the initial velocity, a is the acceleration, and s is the displacement, we can solve for s. Rearranging the equation, we have s = (v^2 - u^2) / (2a). Plugging in the values, we get s = (0 - (98^2)) / (2*(-9.8)) = 490 meters.
19.
A stone is dropped from the roof of a tall building. A person measures the speed of the stone to be 49 m/sec when it hits the ground. The height of the building is closest to:
Correct Answer
C. 122 meters
Explanation
When an object is dropped from a height, it falls freely under the influence of gravity. The speed of the object increases as it falls. The speed at which the stone hits the ground, 49 m/sec, is the final velocity. Using the equation v^2 = u^2 + 2as, where v is the final velocity, u is the initial velocity (which is 0 in this case since the stone is dropped), a is the acceleration due to gravity (approximately 9.8 m/s^2), and s is the distance or height, we can solve for s. Rearranging the equation, we get s = (v^2 - u^2) / (2a). Plugging in the values, we find that the height of the building is closest to 122 meters.
20.
A bolt falls off an airplane high above the ground. How far does the bolt have to fall before its speed reaches 100 m/sec (about 200 miles per hour)? You should ignore air friction in your calculation. (HINT: Calculate time, then calculate distance). You can work this on a piece of paper and turn it in with the test