Physics 20 Review Questions 1. On a trip a motorist travels at 80 km/h for the first 200 km, and 60 km/h for the remainder of the trip. If the trip is 300 km in total, calculate the average speed for the whole trip. [72 km/h] 2. An automobile comes to a stop in 4.0 s. If the vehicle requires 26.7m to come to a stop, what was the initial speed of the vehicle? [13 m/s] 3. An object has an initial speed of 18.0 km/h and a uniform acceleration of 1.50 m/s 2 . How far does the object travel in 20.0 s? [400 m] 4. If a stone is dropped from a cliff, what distance will the rock travel once it reaches a speed of 40.0 m/s? [81.5 m] 5. A stone is thrown vertically upwards at 20 m/s. How long does the stone remain in the air? [4.1 s] 6. A plane can fly at 80.0 m/s in still air. If the plane is traveling north and there is a 25.3 m/s wind from the east, what is the resultant velocity of the plane? [83.9 m/s, 17.5 o W of N or 72.5 o N of W ] 7. A boat with a still water speed of 7.00 m/s is used to cross a river which is 140 m wide and flows at 2.00 m/s. a. What is the resultant velocity of the boat if it starts to head directly across the river? [7.28 m/s, 74.1 o relative to the bank] b. How long does the trip take if the boat starts to head directly across the river? [20.0 s] c. What direction (relative to the bank) must the boat be heading in order to move directly across the river? [73.4 o ]
Transcript
Physics 20 Review Questions1. On a trip a motorist travels at 80 km/h for the first 200 km, and 60 km/h for the
remainder of the trip. If the trip is 300 km in total, calculate the average speed for the whole trip. [72 km/h]
2. An automobile comes to a stop in 4.0 s. If the vehicle requires 26.7m to come to a stop, what was the initial speed of the vehicle? [13 m/s]
3. An object has an initial speed of 18.0 km/h and a uniform acceleration of 1.50 m/s2. How far does the object travel in 20.0 s? [400 m]
4. If a stone is dropped from a cliff, what distance will the rock travel once it reaches a speed of 40.0 m/s? [81.5 m]
5. A stone is thrown vertically upwards at 20 m/s. How long does the stone remain in the air? [4.1 s]
6. A plane can fly at 80.0 m/s in still air. If the plane is traveling north and there is a 25.3 m/s wind from the east, what is the resultant velocity of the plane? [83.9 m/s, 17.5o W of N or 72.5o N of W ]
7. A boat with a still water speed of 7.00 m/s is used to cross a river which is 140 m wide and flows at 2.00 m/s.
a. What is the resultant velocity of the boat if it starts to head directly across the river? [7.28 m/s, 74.1o relative to the bank]
b. How long does the trip take if the boat starts to head directly across the river? [20.0 s]
c. What direction (relative to the bank) must the boat be heading in order to move directly across the river? [73.4o]
8. A ship travels 56.4 m south and then turns and travels 107 m E 43.5o N. What is the net displacement of the ship? [79.5 m N 77.5o E]
9. A 2000kg Mercedes is found 20.0m from the base of a cliff. If the speedometer is stuck at 40.0 km/h and assuming this is the speed at which the car left the road at the top of the cliff, what is the height of the cliff? [15.9 m]
10.A football is thrown at 6.0 m/s 25o relative to the horizontal. a. What is the maximum height reached by the football? [0.33 m]b. How long is the football in the air for? [0.52 s]c. What is the maximum horizontal distance travelled by the football? [2.8 m]
11.The graph below shows the distance of a car versus time. The car is initially heading south. Use the graph below to answer the following questions.
a. When is the car at rest? [from sections B-C and D-E]b. When does the car change directions? [Point E]c. When does the car accelerate? [from section C-D]d. What is the velocity of the car at 180s? [3.75 m/s, north]e. What is the average speed of the car during the 200s? [1.5 m/s]f. What is the average velocity of the car during the 200s? [0.0 m/s]
12.The graph below shows the velocity of a runner versus time. The runner is initially heading east. Use the graph below to answer the following questions.
a. What is the acceleration/deceleration of the runner at 10.0s? [7.5 m/s2, west]
b. What is the acceleration/deceleration of the runner at 13.0s? [0.0m/s2]c. How far did the runner travel after 9.0s? [195 m]d. At what time(s) is the runner at rest? [0.0s & 17s]e. When does the runner change directions? [No change in direction]f. What is the total displacement travelled by the runner? [0.0 m]g. What is the total distance travelled by the runner? [308 m]h. What is the average speed of the runner? [18.1 m/s]i. What is the average velocity of the runner from 0.0s to 9.0s? [22 m/s]
13.Calculate the magnitude of the unbalanced force necessary to accelerate a 4.0kg object 2.0 m/s2. [8.0 N]
14.A 20.0 kg object initially at rest moves 50.0 m in 4.00 s. If the object accelerated uniformly, what was the net force acing on the object? [125 N]
15.A 900 g object is accelerated from rest to 20.9 m/s in 2.20 s. If the frictional force is 1.45 N, what is the applied force? [10.0 N]
16.A 350 g text book is lifted from the floor.a. What is the force applied needed to lift the text book at a constant speed?
[3.43 N]b. A student exerts a force of 5.00N upwards on his text book. What is the
acceleration of his text book? [4.48 m/s2]
17.Bubba has a mass of 60kg. If he wants to make the football team, he needs to have a weight of at least 800N. After some quick thinking, Bubba convinces his coach to take Bubba’s weight in a moving elevator. What must be the acceleration of the elevator for Bubba to make the team? [3.5m/s2, up]
18.Use the following diagram to answer the next questions.
a. What is the acceleration of the 20.0kg mass? [1.96 m/s2 up]b. What is the magnitude of tension in the rope? [235 N]
19.An 8.00kg “Little Rocket” sled is being pulled along level ground by a rope that makes a 40.0o with the horizontal. The sled moves at a constant speed when the force of friction is 8.00N. What is the magnitude of tension in the rope? [10.4 N]
20.Use the following diagram to answer the next questions.
a. Calculate the coefficient of static friction between the surface and a 20.0kg block. [0.577]
b. Once the block is moving, the coefficient of friction drops and becomes 0.450. What is the acceleration of the block along the incline if a force of 400N is used to pull the block up along the incline? [11.3 m/s2, up incline]
30.0kg20.0kg
30.0o
21.Two dogs are pulling on a chew toy. The one dog pulls with a force of 250N, west and the second dog pulls with a force of 600N, 54.0o N of E as shown in the diagram below.
What is the net force on the chew toy as a result of the two dogs? [496N, 78.1o N of E or 11.9o E of N]
22.A 15.0kg pail tied to the end of a rope is whirled around in a vertical circle with a radius of 0.75m. What is tension in the rope at the bottom of the circle if the pail is moving at a speed of 3.35m/s? [3.7x102 N]
23.A pilot wishes to fly in a vertical loop 1.0km in diameter. What is his minimum speed so that he can make it to the top of the vertical loop? [70 m/s]
24.An object has an orbital radius of 5.0m and a mass of 20kg. If it is subjected to a centripetal force of 400N, what is the period of rotation? [3.1 s]
25.What is the orbital period for a satellite at an altitude of 350km above the surface of the earth? [5.49x103 s]
26.What is the gravitational field at a point 2600km from the surface of the earth? [4.95 N/kg or m/s2]
27.What is the weight of a 70kg person who is 152km above the surface of the earth? [6.6x102 N]
28.A student exerts a horizontal force of 225N to push a heavy box along the school corridor at a constant speed of 2.00m/s. How much work does she do in 15.0s? [6.75x103 J]
29.A 15.0kg sled is being pulled along level ground by a rope angled at 36.0o to the horizontal. If the boy uses 25kJ of energy to pull the sled 2.0km home, what is the force exerted through the rope? [15 N]
30.When a 2.0kg mass is hung from a spring, it stretches 11 cm. How much elastic potential energy is stored in the spring when the mass is hung from it? [1.1 J]
31.By what factor will the kinetic energy of an object change if the speed is halved and the mass is tripled? [by a factor of 3/4]
32.An object is dropped from a height of 10.0m above the ground. Calculate the speed of the object as it hits the ground? [14 m/s]
33.A 20.kg object is thrown vertically downward at a speed of 5.0m/s from a height of 12.0m above the ground. Calculate the speed of the object as it hits the ground. [16 m/s]
34.A pendulum bob is held 76 cm above its point of equilibrium. The bob is then released. What is the maximum speed of the pendulum bob as it passes through its equilibrium point? [3.9 m/s]
35.The spring in a dart gun has a spring constant of 1.2x103 N/m. If the spring is compressed 10cm, what is the horizontal speed of the 100g dart if it was fired horizontally? [11 m/s]
36.A roller coaster travels from point A to point B along a frictionless track as shown in the diagram. If the speed of the roller coaster is 11m/s at point B, what is the speed at point A? [1.8 m/s]
37.A 11.7kg box is pushed 15.0m up along a 20.0o incline. The force used to push the box 15.0m up along the incline is 350N. What is the energy lost due to friction? [3.63x103 J]
38.A crane raises 1700kg of rock 80.0m high at a constant speed in a total time of 2.00 minutes. What is the power required by the crane’s motor? [1.11x104 W]
39.A pendulum is formed by hanging a mass from a string 2.00m in length. What is the frequency for this pendulum? [0.352 Hz]
40.A 1.00kg object vibrates at the end of a vertical spring. If the frequency of the vibration is 1.25 Hz, what is the spring constant? [61.7 N/m]
41.27.0N is required to stretch a spring 5.1cm. What will be the period of this spring if a 6.22kg mass is attached to the end? [0.68 s]
42.10 waves break on the beach in 1.5 minutes. What is the frequency of these waves? [0.11 Hz]
43.A student is at the edge of a canyon that is 260m wide. If the student calls out, she can hear her echo 1.5s later. What is the speed of the sound waves? [3.5x102 m/s]
44.An opened air column resonates with a fundamental frequency of 512 Hz. If the length of the air column is 33.0cm, what is the speed of the sound wave? [338m/s]
45.An air column closed at one end resonates with a fundamental frequency of 384Hz. If the speed of sound is 341m/s, what is the length of the air column? [22.2 cm]
46.A 384Hz tuning fork is held over a closed pipe resonator. If the speed of the sound is 343m/s, what is the spacing between the resonances points (the distance between two successive loud sounds)? [0.447 m]
47.A train is moving towards you at 23.1m/s. You hear a frequency of 275 Hz. What is the actual frequency of the train whistle if the speed of sound in air is 341m/s? [256 Hz]
