PHY200-1
How much force must a locomotive exert on a 13800-kg boxcar to make it accelerate forward at 0.32 m/s2?
4.41 kN
You're squeezing a springy rubber ball in your hand. If you push inward on it with a force of 1 N, it dents inward 1 mm. How far must you dent it before it pushes outward with a force of 7 N?
7 mm
A tricycle releases 40 J of gravitational potential energy while rolling 0.55 m directly downhill along a ramp. What is the downhill force (if constant) acting on the tricycle?
72.77 N
Suppose your car is on a 5% grade, meaning that for every 100 m you travel along the road you raise or lower only 5 m in elevation. If your car weighs 1500 kg, what is the component of its weight parallel to the road?
750 N
How much does a 79-kg person weigh on earth?
774 M
The kicker in a sporting event isn't always concerned with how far downfield the ball travels. Sometimes the ball's flight time is more important. If he wants to keep the ball in the air as long as possible, he should kick it
at a large angle from the ground.
Let your car have a mass of 881 kg. Your car is moving at a speed of 3.91 m/s when it strikes a parked car and stops in 0.14 s. What force did the parked car exert on it to stop it that quickly?
24.6 kN
When the man, who weighs 950 N, stands on a particular trampoline, its springy surface shifts downward 0.1 m. If he bounces on it so that its surface shifts downward 0.26 m, how hard is it pushing up on him?
2470 N
On Mars, the acceleration due to gravity is 3.71 m/s2. How far would a rock fall in 4 s if you dropped it on Mars?
29.7m
What is the momentum of a fly if it's traveling 2.0 m/s and has a mass of 0.00019 kg?
3.8e-4 kg-m/s
If your car has a mass of 872 kg, how much force is required to accelerate it forward at 3.63 m/s2?
3139 N
Your car is broken, so you're pushing it. If your car has a mass of 811 kg, how much momentum does it have when it's moving forward at 4.52 m/s (16.3 km/h)?
3665.7 kg-m/s
You're sanding a table. You must exert a force of 38 N on the sandpaper to keep it moving steadily across the table's surface. You slide the paper back and forth for 23 minutes, during which time you move it 1000 m. How much work have you done?
38 kJ
If you jump upward with a speed of 2.2 m/s, how long will it take before you stop rising?
.22s
A speedboat is pulling a water-skier with a rope, exerting a large forward force on her. The skier is traveling in a straight line at constant speed. The net force she experiences is
0
Two teams are having a tug-of-war with a sturdy rope. It has been an even match so far, with neither team moving. What is the net force on the left team?
0
You are riding a bicycle into a strong head wind, but manage to keep moving in a straight line at a constant speed. The net force on you is
0
If an 82-kg baseball pitcher wearing frictionless roller skates picks up a 0.145-kg baseball and pitches it toward the south at 46 m/s, how fast will he begin moving toward the north?
0.081 m/s
When you put water in a kitchen blender, it begins to travel in a 4-cm-radius circle at a speed of 1 m/s. How hard must the sides of the blender push inward on 0.004 kg of the spinning water?
0.1 N
If you jump upward with a speed of 2.8 m/s, how high will you be when you stop rising?
0.400m
The gravity of a black hole is so strong that not even light can escape from within its surface or "event horizon." Even outside that surface, enormous energies are needed to escape. Suppose that you are 5 km away from the center of a black hole that has a mass of 1031 kg. If your mass is 67 kg, how much do you weigh?
1.78e15 N
An elevator releases 10900 J of gravitational potential energy while descending 7 m between floors. How much does the elevator weigh?
1.557 kN
An antique carousel that's powered by a large electric motor undergoes constant angular acceleration from rest to full rotational speed in 5 seconds. When the ride ends, a brake causes it to decelerate steadily from full rotational speed to rest in 8.6 seconds. Compare the torque that starts the carousel to the torque that stops it.
1.7
The builders of the pyramids used a long ramp to lift 20000-kg (20-ton) blocks. If a block rose 1.2 m in height while traveling 22 m along the ramp's surface, how much uphill force was needed to push it up the ramp at constant velocity?
10.68 kN
You're using a wedge to split a log. You are hitting the wedge with a large hammer to drive it into the log. It takes a force of 3400 N to push the wedge into the wood. If the wedge moves 0.3 m into the log, how much work have you done on the wedge?
1020 J
You begin pushing the car forward from rest. Assume that your car has a mass of 846 kg. Neglecting friction, how long will it take you to push your car up to a speed of 3.48 m/s on a level surface if you exert a constant force of 247 N on it?
11.9 s
When you ride a bicycle, your foot pushes down on a pedal that's 18.4 cm (0.184 m) from the axis of rotation. Your force produces a torque on the crank attached to the pedal. Suppose that you weigh 621 N. If you put all your weight on the pedal while it's directly in front of the crank's axis of rotation, what torque do you exert on the crank?
114 Nm
The builders of the pyramids used a long ramp to lift 21000-kg (21-ton) blocks. How much work was done in raising one of the blocks to a height of 56 m?
11524 kJ
Your new designer chair has an S-shaped tubular metal frame that behaves just like a spring. When your friend, who weighs 590 N, sits on the chair, it bends downward 5 cm. What is the spring constant for this chair?
11800 N/m
The tire of your bicycle needs air so you attach a bicycle pump to it and begin to push down on the pump's handle. If you exert a downward force of 25 N on the handle and the handle moves downward 0.5 m, how much work do you do?
12.5 J
A sprinter can reach a speed of 12 m/s in 0.94 s. If the sprinter's acceleration is constant during that time, what is the sprinter's acceleration?
12.76 m/s^2
An electric saw uses a circular spinning blade to slice through wood. When you start the saw, the motor needs 3 seconds of constant angular acceleration to bring the blade to its full angular velocity. If you change the blade so that the rotating portion of the saw now has 4 times its original rotational mass, how long will the motor need to bring the blade to its full angular velocity?
12s
The builders of the pyramids used a long ramp to lift 22000-kg (22-ton) blocks. What is the gravitational potential energy of one of the blocks if it's now 80 m above the ground?
17245 kJ
As water descends from the top of a tall hydroelectric dam, its gravitational potential energy is converted to electric energy. How much gravitational potential energy is released when 1200 kg of water descends 150 m to the generators?
1764 kJ
On Mars, the acceleration due to gravity is 3.71 m/s2. What would a rock's velocity be 5 s after you dropped it on Mars?
18.55 m/s
A gymnast jumps upward with an initial speed of 10 m/s. She is in the air for a total time of
2 seconds.
If you and a friend 14 m away each have masses of 77 kg, how much gravitational force are you exerting on your friend?
2.02 x 10^-9 N
How high above the earth's surface would you have to be before your weight would be only 0.5 its current value? (Note: The earth's radius is 6378 km.)
2.64 x 10^6 m
If a sprinter's mass is 56 kg, how much forward force must be exerted on the sprinter to make the sprinter accelerate at 0.73 m/s2?
40.88 N
You're at the roller-skating rink with a friend who weighs twice as much as you do. The two of you stand motionless in the middle of the rink so that your combined momentum is zero. You then push on one another and begin to roll apart. If your momentum is then 475 kg·m/s to the left, what is your friend's momentum?
475 kg-m/s to the right.
When you put water in a kitchen blender, it begins to travel in a 8-cm-radius circle at a speed of 2 m/s. How quickly is the water accelerating?
50 m/s^2
Your suitcase weighs 50 N. As you ride up an escalator toward the second floor, carrying that suitcase, you are traveling at a constant velocity. The upward force you must exert on the suitcase to keep it moving with you is
50N
If your car accelerates from rest at a steady rate of 4 m/s2, how soon will it reach 88 km/h (54.7 mph or 24.4 m/s)?
6.10s
A basketball player can leap upward 0.64 m. What is his initial velocity at the start of the leap?
6.54 m/s
Locomotive exert on a 12160-kg boxcar to make it accelerate forward at 0.49 m/s2. How long will it take the boxcar to reach its cruising speed of 117 km/h (72.7 mph or 32.5 m/s)?
66s
When you push down on the handle of a doll-like wooden nutcracker, its jaw pivots upward and cracks a nut. If the point at which you push down on the handle is 4 times as far from the pivot as the point at which the jaw pushes on the nut, how much force will the jaw exert on the nut if you exert a force of 20 N on the handle? (Assume that all forces are at right angles to the lever arms involved.)
80 N
The earth exerts a downward force of 850 N on a veteran astronaut as he works outside the space shuttle. What force (if any) does the astronaut exert on the earth?
850 N upward.
You roll a marble down a playground slide that starts level, then curves downward, and finally the curve flattens out so that it's level again at the end. Where along its travel does the marble experience its greatest acceleration?
Along the downward curve.
When you apply the brakes on your bicycle, which way do you accelerate?
Backward.
Why is your velocity continuously changing as you ride on a carousel?
Because your direction of motion is continuously changing.
When you kick a soccer ball, which pushes on the other harder: your foot or the soccer ball?
Both Push Equally.
Firefighters slide down a pole to get to their trucks quickly. What happens to their gravitational potential energy, and how does it depend on the slipperiness of the pole?
It converts to kinetic energy and thermal energy of their hands and the pole. A slippery pole will result in more kinetic and less thermal energy.
Suppose a tree branch falls down to the ground with constant acceleration and takes 2 seconds to hit the ground. Which of the following statements regarding the path of the branch is true?
It covers more distance during the last second.
Tightrope walkers often use long poles for balance. Although the poles don't weigh much, they can exert substantial torques on the walkers to keep them from tipping and falling off the ropes. Why are the poles so long?
Longer poles mean larger torques.
As you jump across a small stream, does a horizontal force keep you moving forward? If so, what is the force?
No, there is no horizontal force. You continue to move forward because of inertia.
A common pair of pliers has a place for cutting wires, bolts, or nails. Why is it so important that this cutter be located very near the pliers' pivot?
Small lever arm means large force.
Comic book superheroes often catch a falling person only a hairsbreadth from the ground. Why would this rescue actually be just as fatal for the victim as hitting the ground itself?
The acceleration required to stop in such a short time is still huge, so the force required would be huge.
Why can't you open a door by pushing its doorknob directly toward or away from its hinges?
The force here is parallel to the lever arm, not perpendicular.
Suppose you have two cars, and the larger one is twice as massive as the smaller one. If you and a friend push on them so that their accelerations are equal, how must the forces applied to the cars compare?
The force on the larger car is twice that on the smaller car.
If you are pulling a sled along a level field at constant velocity, how does the force you are exerting on the sled compare to the force of sliding friction on its runners?
The force you exert is equal to the sliding friction.
Which is larger: the force the earth exerts on you or the force you exert on the earth?
The forces are equal.
Skiers often stop by turning their skies sideways and skidding them across the snow. How does this trick remove energy from a skier, and what happens to that energy?
The friction of skidding converts the skier's energy into thermal energy.
Why can't you open a door by pushing on its hinged side?
The lever arm is zero.
One way to crack open a walnut is to put it in the hinged side of a door and then begin to close the door. Why does a small force on the door produce a large force on the shell?
The small force on the door has a large lever arm, but the force on the walnut has a small lever arm.
A ball falls from rest for 5 seconds. Neglecting air resistance, during which of the 5 seconds does the ball's speed increase most?
The speed change is the same during each of the 5 seconds.
How does a bottle opener use mechanical advantage to pry the top off a soda bottle?
The torque of your hand on the bottle opener is equal to the torque of the bottle opener on the bottle cap.
Driving down the road, you hit an insect. How does the force your car exerts on the insect compare to the force the insect exerts on the car?
The two forces are equal in magnitude.
When an airplane starts its propellers, they spin slowly at first and gradually pick up speed. Why does it take so long for them to reach their full rotational speed?
They have a large rotational mass.
Loose objects on the dashboard slide to the right when the car turns suddenly to the left because
They have inertia.
The back of your car seat has a head rest to protect your neck during a collision. The type of collision which causes your head to press against the headrest is
a rear-end collision.
A metro train is traveling at constant velocity. What are the net forces on (a) the first car, (b) the middle car, and (c) the last car?
a. 0 b. 0 c. 0
The gravity of a black hole is so strong that not even light can escape from within its surface or "event horizon." Even outside that surface, enormous energies are needed to escape. Suppose that you are 6 km away from the center of a black hole that has a mass of 1031 kg. Your mass is 78 kg, how much work would something have to do on you to lift you 1 m farther away from the black hole?
a=14.5 x 10^14 J
A car passes by, heading to your left, and you reach out and push it toward the left with a force of 50 N. Does this moving car push on you and, if so, with what force?
Yes, 50 N to the right.
A projectile is thrown directly upward and caught again. At the top of its path
its vertical velocity is zero
You throw brick straight up. Ignoring air resistance, after it leaves your hand it will experience
only the downward force of its weight, both before and after it reaches its maximum height.
The chairs in an auditorium aren't all facing the same direction. How could you describe their angular position in terms of a reference orientation and a rotation?
radians clockwise from north
A gristmill is powered by falling water, which pours into buckets on the outer edge of a giant wheel. The weight of the water turns the wheel. It is important that the buckets be on the wheel's outer edge because
that maximizes the lever arm.
A dolphin can leap several meters above the ocean's surface. Gravity does not stop the dolphin from leaving the water because
the dolphin has inertia as it approaches the surface.
It's much easier to carry a weight in your hand when your arm is at your side than it is when your arm is pointing straight out in front of you. Use the concept of torque to explain this effect. When you arm is at your side
the force is parallel to the lever arm, not perpendicular.
A satellite is orbiting the earth just above its surface. The centripetal force making the satellite follow a circular trajectory is just its weight, so its centripetal acceleration is about 9.81 m/s2 (the acceleration due to gravity near the earth's surface). If the earth's radius is about 6370 km, how fast must the satellite be moving? How long will it take for the satellite to complete one trip around the earth?
v = 7.9 km/s time= 84 min
How would your Mars weight compare to your earth weight if the acceleration due to gravity on Mars is 3.71 m/s2?
wmars/wearth = 37.8%