AP Physics 1 – Ch6,7 Homework
Ch6 HW#1 p205 1,5,11,16,19,20,22,23
1. While floating out in space, a constant force of 500 N is applied to a 542.3-kg robot by a small rocket motor.
The robot moves along a straight line in the direction of the thrust of the motor. How much work is done on it
by the rocket for every 10.0 meters traveled?
5. A book is slowly slid in a straight line, at a constant speed, 1.5 m across a level table by a 15 N horizontal
force. How much work is done on the book-table system and what is it done against?
11. A nurse pushes someone in a wheelchair 100m doing 400 J of work in the process. What average force did
the nurse exert in the direction of motion?
16. A pickup truck is hauling a barge along a canal at a constant speed. The truck, driving parallel to the
waterway at a 30º angle with the forward direction. If the truck exerts a force of 1000 N on the cable, how
much work is done in overcoming friction as the barge is moved 10 km?
19. A 100 N box filled with books is slid along a 13 m long ramp up to a platform 5.0 m above the ground.
How much work is done if friction is negligible? How much work would have been done if the box were lifted
straight up to the platform?
20. Several crates, having a total weight of 400 N, are loaded into a 10.0 kg wagon that is then pulled up a
wooden ramp 10.0 m long making an angle of 30.0o. If friction was negligible, how much work was done?
22. A 50 kg keg of beer sits on a platform 1.5 m above the ground. It slides down a 3.0 m long plank down to the
ground. Determine the amount of work done on the keg by gravity.
23. A newspaper delivery boy pulls horizontally on a rubber-wheeled cart that has a coefficient of rolling friction
of 0.02 and a mass of 25 kg. It travels 10 km on level streets.
a. How much work does he do in overcoming friction between the cart and the ground?
If he pulls his cart 25 m along a road inclined at 10˚,
b. how much work does he do to overcome road friction?
c. how much work overcoming gravity?
Ch6 HW#2 Practice Graphs
1. A force is gradually placed on an object,
uniformly increased to 20 N over a distance of 5 m.
It then stays constant for the next 5 m.
How much work was done on this object?
2. A force of 10 N is applied to an object over a distance of 3 m,
and then is uniformly increased to 15 N while the object moves
a distance of 4 m. How much work is done on the object?
3. A 0.20 kg object moves along a straight line. The net force
acting on the object varies with the object’s displacement
as shown. The object starts from rest at displacement x = 0
and time t = 0 and is displaced a distance of 20 m.
Determine each of the following.
a. The accl of the particle when its displacement x is 6 m
b. The time taken for the object to be displaced the first 12 m
c. The amount of work done displacing the object the first 12 m
d. The speed of the object at displacement x = 12 m
e. The final speed of the object at displacement x = 20 m
Ch6 HW#3 p207+ 28,34,38,41,44,47,55
28. The record average speed for the men’s 10 km walk is 4.4 m/s. How much kinetic energy would a 70 kg
athlete have at that speed?
34. Suppose that a 0.149 kg baseball is traveling at 40.0 m/s. How much work must be done on the ball to stop
it? If it’s brought to rest in 2.0 cm, what average force must act on the ball?
38. A video of a 70.0 kg male sprinter shows him going from zero to 3.0 m/s on the first step, reaching 4.2 m/s
on the second step, and 5.1 m/s on the third step. Compare the speed and energy gained in each step.
41. A 0.046 kg golf ball is driven from rest to 70.0 m/s in about 1.0 ms. Determine the kinetic energy of the ball,
and approximate the distance over which the club acted on the ball.
44. The energy content of beer is about 1.8x10 6 J/kg. If that energy could be turned completely into
gravitational-PE, how much beer would we need to raise a 1.0 kg mass 1.0 km into the air?
47. A car with a mass of 1000-kg is at rest at the base of a hill. It accelerates up the incline reaching a speed of
20 m/s at a height of 100 m. What is the total increase in mechanical energy (KE plus PE G) at that point?
55. There are three identical flat stone blocks each 0.50 m high lying on the ground. What is the increase in
gravitational potential energy when the blocks are stacked one on top of the other to a height of 1.50 m?
Each block weighs 1000 N.
Ch6 HW#4 p209 59,60,61,62,63
59. What is the kinetic energy of a 10.0kg piece of concrete after it has fallen for 2.00sec from the side
of an old building?
60. A 60kg stunt person runs off a cliff at 5.0m/s and lands safely in the river 10.0m below.
What is the splashdown speed?
61. Two automobiles of weight 7.12kN and 14.24kN are traveling along horizontally at 96 km/h (26.7 m/s)
when they both run out of gas. Luckily, there is a town in a valley not far off, but it’s just beyond a 33.5 m
high hill. Neglect friction, which of the cars will make it to town?
63. A kid in a wagon is traveling at 10 m/s just as she reaches the bottom of a hill and begins to climb a second
hill. How high up it will she get before the wagon stops, assuming negligible friction losses?
Ch6 HW#5 p209 74 + 2 Bonus questions
Bonus #1. A 5kg object starts at rest, slides down an incline plane
with a kinetic coefficient of friction of 0.10, as shown.
What is the speed at the bottom of the incline?
Bonus #2. A 2kg object starts at rest, slides down an incline plane,
as shown. If its speed at the bottom is 2.78 m/s,
what is the kinetic coefficient of friction?
74. An inclined plane at 30.0º is 6.40m long. A book, which has a kinetic coefficient of friction with the incline
of 0.20, is placed at the top and immediately begins to slide. Using energy considerations, how long will it
take for the book to reach the bottom of the incline?
Ch6 HW#6 p210 78,79,81,87,93
78. How much power does it take to raise an object weighing 100N a distance of 20.0m in 50s?
79. A runner traverses a 50m long stretch on a horizontal track in 10s at a fairly constant speed. All the while
she experiences a retarding force of 1.0N due to air friction. What power was developed overcoming friction?
81. The per capita power consumption in the United States is around 10kJ each and every second. At what
speed would you have to push a car exerting a force of 1.0kN on it all year, day in and day out, to be
equivalent to your share?
87. A 2.5 hp motor drives a hoist that can raise a load of 50kg to a height of 20m. How long will it take to do it?
93. A 2x103 kg spacecraft has a ion engine that delivers 150kW of propulsive power via its six thrusters.
How much time would it take to accelerate from “rest” to 268 m/s (i.e. 600 mi/h)?
Ch7 HW#1 p235 2,3,4,6,7,11,13,14
2. What is the momentum of the Earth (m=5.975x10 24 kg) as it moves through space if its orbital speed is about
66,600mph (multiply 66,600mph x 0.4470 to get m/s)
3. A 1.0kg wad of clay is slammed straight into a wall at a speed of 10 m/s.
If the clay sticks in place, what was the impulse that acted on it via the wall?
4. What is the impulse provided by the racket on a tennis ball (0.058 kg) served at 50 m/s?
6. A dried pea fired from a plastic drinking straw has a mass of 0.50 g. If the force exerted on the pea is an
average 0.070lb (multiply 0.070lb x 4.448 to get Newtons) over the 0.10s flight through the straw,
at what speed will it emerge?
7. A 1.0kg body initially traveling in the positive x-direction at 10 m/s is acted upon for 2.0 s by a force in the
same direction of 20 N. It then experiences a force acting in the negative direction for 20s equal to 2.0 N.
Draw a force-time curve and determine the final momentum.
11. A youngster having a mass of 50.0 kg steps off a 1.00 m high platform. If she keeps her legs fairly rigid and
comes to rest in 10.0 ms, what is her momentum just as she hits the floor? What average force acts on her
during the subsequent deceleration?
13. A 47 g golf ball is hit in the air at 60 m/s. It lands in sand at the same elevation and comes to rest in 10 ms.
Ignoring air friction, what was the average force the sand exerted on the ball?
14. A golf ball with a mass of 47.0 g can be blasted from rest to a speed of 70.0 m/s during the impact with a
club head. Taking that impact to last only about 1.00 ms, calculate the change in momentum of the ball.
Ch7 HW#2 p236 19,22 + 3 Bonus Questions
19. A nuclear aircraft carrier weighs 90,000 tons (82 million Newtons) and can travel at 30 knots (15m/s).
If it plows into a pier and comes to rest in 0.50min, what average force does it exert on the pier?
22. A typical tubular aluminum arrow 70-cm long has a mass of 25.0 g. The force exerted by a bow varies in a
fairly complicated fashion from the initial draw force of, say, 175N (39 lb) to zero, as the arrow leaves the
string. Assume a full draw (70 cm) and a launch time of 16.0 ms. If the arrow when fired straight up reaches
a maximum height of 143.3 m above the point of launch, then (a) What is the average force exerted on it by
the bow? (b) What’s the area under the force-time curve? (c) What impulse is applied to the shooter?
Bonus #1. A 0.149kg baseball is traveling south at 35 m/s,
when it is hit by a bat, exerting a varying force lasting 3ms,
as shown in the diagram. What is the ball’s final speed.
Bonus #2. A 10kg curling puck starts at rest and is pushed
by a ‘curler’, for 3 seconds,
by a force that follows a fairly complicated fashion, #1.
#2.
as shown. What is the release speed of the puck?
Bonus #3. For each of the graphs shown, describe any
physical meaning for:
1) slope of each line or 2) area under each curve
#3.
Ch7 HW#3 p236 25,26,27,28,30,37
25. A rocket engine blasts out 1000 kg of exhaust gas at an average speed of 2 km/s every second.
Calculate the resulting average thrust developed by the engine.
26. Water squirting from a hose emerges with a speed of 10 m/s at a rate of 100 kg/s. Compute the average
reaction force exerted on the hose. Have you ever seen firefighters working to control a large hose?
27. A 50 kg person at the southernmost end of a 150 kg rowboat at rest in the water begins to walk to the
northern end. If, at a given instant, her speed with respect to the water is 10 m/s, what is the velocity of the
boat with respect to the water at that moment?
28. While constructing a space platform a 100 kg robot finds himself standing on a 30 m long 200 kg steel beam
that is motionless with respect to the platform. Using his magnetic feet he walks along the beam traveling
south at 2.00 m/s. What is the velocity of the beam with respect to the platform as the robot walks?
30. While floating in space a 100 kg robot throws a 0.800 kg wrench at 12.0 m/s toward his partner working on
the spaceship. How fast will the robot move away from the ship?
37. An ice skater (with a mass of 55.0 kg) throws a snowball while standing at rest. The ball has a mass of 200g
and moves straight out with a horizontal speed of 20.0 km/h. Neglecting friction, and assuming the skate
blades are parallel to the direction of the throw, describe the skater’s resulting motion in detail.
Ch7 HW#4 p237+ 39,44,45,46,47,51,54 (Modified)
39. A railroad flatcar having a mass of 10,000 kg is coasting along at 20m/s. As it passes under a bridge,
10 men (having an average mass of 90 kg) drop straight down onto the car. What is the speed as it emerges
with its new passengers from beneath the bridge?
44. Two identical cars of mass 2000 kg each drive toward one another, both traveling at 20.0 m/s.
They collide head-on and smash together; what is the final speed of the wreckage?
45. A glider on an air track has a mass of 1.00 kg and floats on compressed air, so it can move frictionlessly.
Someone shoots a 20.0 g lump of clay at it. The clay strikes the glider, sticks to it, and both move away with
a speed of 20.0 cm/s. What was the speed of the clay as it hit the glider?
46. Two wads of putty are propelled horizontally directly toward each other. Wad-1 has a mass of 5.00 kg and is
traveling at 21.0 m/s south. Wad-2, which is 6.00 kg, is moving at 12.0m/s north. They collide and stick
together. What is the velocity of the joint mass of putty?
47. A 1263 kg Triumph TR-8 sports car traveling south at 40 km/h (11.6 m/s) crashes head-on into a 1742kg
Checker cab moving north at 90 km/h (25 m/s). If the two cars remain tangled together but free to coast,
describe their motion immediately after collision. What is their final speed? How much kinetic energy is lost?
51. A 90 kg signal relay floating in space is struck by a 1000 g meteoroid. The latter imbeds itself in the craft
and the two sail away at 5.0 m/s. What was the initial speed of the meteoroid?
54. Two 10.0kg blocks are to be used in an experiment on a frictionless
surface. The first is held at rest on a 20.0° inclined plane 10.0 m from
the second, which is at rest at the foot of the plane.
a. What is the speed of m1 at the bottom of the incline?
b. m1 slams into and sticks to m2, what is their speed after the collision?
c. When this experiment is conducted, it is found that they do not stick
together, and m2 is measured to have a speed of 6.1 m/s.
What is the speed of m1?
Ch7 HW#5 p235 5,9,29,53,55
5. During a game a soccer ball having a mass of 0.425 kg is kicked from rest to 26 m/s in a collision with a
player’s foot lasting 8 ms. What is the impulse imparted to the ball?
9. If a 0.061kg handball goes from rest to 20 m/s during a serve and the player feels an average force of 100 N,
how long did the impact last?
29. The glider on an air track is 30.0 cm long and has a mass of 0.500 kg.
It floats frictionlessly on compressed air and is free to move along an east-west axis.
A 100 g wind-up toy car is placed on the glider and it immediately rolls due east
at 0.50 m/s with respect to the lab. Does the glider move, how fast and what dir?
53. An 8.0 kg puck floating on an air table is traveling east at 15 cm/s. Coming the other way at 25 cm/s is a
2.0 kg puck on which is affixed a wad of bubblegum. The two slam head-on into each other and stick
together, find their velocity after the impact. How much kinetic energy is lost?
55. (Modified) An 8.0 kg puck floating on an air table is traveling east at 15 cm/s. Coming the other way
at 25 cm/s is a 2.0 kg puck, no bubblegum. The two slam head-on into each other and the 2.0 kg puck
bounces backward at 20 cm/s. What is the speed and direction of the 8.0 kg puck?
How much kinetic energy is lost?
Ch7 HW#6 p238 58,59,60
58. A skater with a mass of 75kg is travelling east at 5 m/s when he collides
with another skater of mass 45kg heading 60° south of west at 15 m/s.
If they stay tangled, what is their final speed?
59. A soft clay block is suspended so as to form a ballistic pendulum.
A bullet is fired into the clay, raising the pendulum to a height h.
Write an expression for the muzzle speed in terms of g, h, and their masses.
60. Derive an expression for the percentage of kinetic energy converted into
internal energy during the clay-bullet impact.
Ch6 Rev p205+ 4,21,35,42,50,68(mod),80
4. What is the work done by gravity when a 2.0-kg ball falls on the floor from a height of 1.50 m? Is it (+ or -)?
21. Starting from rest, a 25.0 kg kid runs up a 5.0 m long slide. At the end he is standing still 3.0 m higher than
at the start, how much work did he do?
35. The shot used by male shot-putters has a mass of 7.26 kg. A good throw (which might go roughly 23 m)
would correspond to a launch at about 14 m/s. Determine the shot’s kinetic energy and compare that to the
kinetic energy of a 149 g baseball thrown at a record pitching speed of 45 m/s. Can you explain the
difference, that is, where does that energy difference go when a baseball is thrown - surely the pitcher is
trying just as hard as the shot putter.
42. What is the kinetic and potential energy of a Boeing 747 airliner weighing 2.22x10 6 N, flying at 268 m/s
(i.e. 600 mi/h) at an altitude of 6.1 km (i.e. 20,000 ft)?
50. A 10.0 kg package is raised from rest by an elevator at a constant acceleration of 2.00 m/s 2 for 20.0s.
(a) What is its KE at t=10.0 s?
(b)What is its increase in gravitational potential energy after 10.0 s?
(c)Assuming no losses, how much work has done on it by the elevator in 10.0 s?
68. A 100 kg car racing towards a mountain at 50m/s runs out of gas. Cleverly, the driver shifts into neutral
and coasts onward. Neglecting all friction losses, will he clear the 65 m peak? Speed at top?
80. A small hoist can raise 100 kg of bricks to the top of a construction project 30 m above the street in half a
minute. Determine the power provided.
(Maybe look at this one again)
74. An inclined plane at 30.0º is 6.40 m long. A book, which has a kinetic coefficient of friction with the incline
of 0.20, is placed at the top and immediately begins to slide. Using energy considerations, how long will it
take for the book to reach the bottom of the incline?
Ch7 Rev p235 12,37,56
12. A 20.0 kg ball of clay drops off a scaffold and falls for 4.0 s before hitting the ground. If it comes to rest
in 5.0 ms, what average force did the floor exert on the clay? Use momentum to solve the problem.
37. An ice skater with a mass of 55.0 kg throws a snowball while standing at rest. The ball has a mss of 200 g
and moves straight out with a horizontal speed of 20.0 km/h, Neglecting friction, and assuming the skate
blades are parallel to the direction of the throw, describe the skater’s resulting motion in detail.
56. As seen from the window of a space station, a 100 kg satellite sailing along at 10.0 m/s collides head on with
a small 300 kg asteroid, which was initially at rest. Taking the collision to be inelastic, and neglecting their
mutual gravitational interaction, what is the final velocity of the two bodies?