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Physics 101 Mechanics
November 2021
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Physics 101 Mechanics
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November 27, 2021
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November 27 of 2021
Data for one stage of the 2004 Tour de France show that Lance Armstrong’s average speed was 15 m/s, and that keeping Lance and his bike moving at this zippy pace required a power of 450 W. What was the average forward force keeping Lance and his bike moving forward? To put this in…
A typical human head has a mass of 5.0 kg. If the head is moving at some speed and strikes a fixed surface, it will come to rest. A helmet can help protect against injury; the foam in the helmet allows the head to come to rest over a longer distance, reducing the force on the head. The foam…
In a typical tee shot, a golf ball is hit by the 300 g head of a club moving at a speed of 40 m/s. The collision with the ball happens so fast that the collision can be treated as the collision of a 300 g mass with a stationary ball—the shaft of the club and the golfer can be ignored. The…
The electric force of repulsion between two electrons is similar to the gravitational force [ Fe=k(q1q2/r^2) ], where k is called Planck’s constant, q is the charge on a particle, and r is the distance separating the charges. Don’t look up the value of k. We’re not looking for an exact…
Spring into action A locust can jump as far as 1 meter, an impressive distance for such a small animal. To make such a jump, its legs must extend much more rapidly than muscles can ordinarily contract. Thus, instead of using its muscles to make the jump directly, the locust uses them to…
A 2.0 g desert locust can achieve a takeoff speed of 3.6 m/s (comparable to the best human jumpers) by using energy stored in an internal “spring” near the knee joint. When the locust jumps, what energy transformation takes place? What is the minimum amount of energy stored in the…
A 200 g block on a frictionless surface is pushed against a spring with spring constant 500 N/m, compressing the spring by 2.0 cm. When the block is released, at what speed does it shoot away from the spring?
A car sits at rest at the top of a hill. A small push sends it rolling down a hill. After its height has dropped by 5.0 m, it is moving at a good clip. Write down the equation for conservation of energy, noting the choice of system, the initial and final states, and what energy…
When you run a heat engine, some (or most) of the energy is “wasted” as heat transferred to the cold reservoir. Suppose someone suggests making a 100% efficient heat engine by using some of the output of the heat engine to run a heat pump to transfer this heat back to the hot reservoir.…
A typical gasoline-powered car stops by braking. Friction in the brakes brings the car to rest by transforming kinetic energy to thermal energy. Electric vehicles often stop by using regenerative braking, with the engine used as a generator, transforming the kinetic energy of the vehicle…
At The Geysers geothermal power plant in northern California, electricity is generated by using the temperature difference between the 15 °C surface and 240 °C rock deep underground. What is the maximum possible efficiency? What happens to the energy that is extracted from the steam that is…
A container holds 4.0 x 1022 molecules of an ideal gas at 0 °C. A piston compresses the gas, doing 30 J of work. At the end of the compression, the gas temperature has increased to 10 °C. During this process, how much heat is transferred to or from the environment?
The air in a typical bedroom consists of about 8.0 x 1026 atoms. Suppose a small fan is running, using 50 W. And suppose that there is no other transfer of energy, as work or heat, into or out of, the air in the room. By how much does the temperature of the room increase during 10 minutes…
Using a fan to move air in a room will make you feel cooler, but it will actually warm up the room air. A small desk fan uses 50 W of electricity; all of this energy ends up as thermal energy in the air of the room in which it operates.
How far could a 68 kg person cycle at 15 km/hr on the energy in one slice of pizza? How far could she walk, at 5 km/hr? How far could she run, at 15 km/hr? Do you notice any trends in the distance values that you’ve calculated? Chemical energy from food is used for each of these activities.…
A 75 kg person climbs the 248 steps to the top of the Cape Hatteras lighthouse, a total climb of 59 m. How many Calories does he burn?
A person lifts a 20 kg box from the ground to a height of 1.0 m. A metabolic measurement shows that in doing this work her body uses 780 J of energy. What is her efficiency?
Light bulbs are rated by the power that they consume, not the light that they emit. A 100 W incandescent bulb emits approximately 4 W of visible light. What is the efficiency of the bulb?
Why can you not hear your distant neighbor's conversations in the winter?
Explain how you can lower the pitch of a note on a guitar by changing the string's length. If desired play a lower note, what would you do to the tension?
Enumerate various scenarios/cases of non-uniform stress distribution in solids. Explain with the help of examples why simple stress definition cannot be used in such cases.
Calculate the torque (magnitude and direction) about point O due to the force F? in each of the cases sketched in the figure (Figure 1). In each case, the force F? and the rod both lie in the plane of the page, the rod has length 4.00 m, and the force has magnitude 15.0 N .
A body having a mass of 20 kg rests on a surface inclined 30° to the horizontal. Assume a coefficient of friction of 0.76 and calculate the magnitude of the force F, acting at an angle of 40° with the inclined surface required to: a) Pull the body upwards; b) Pull the body downwards; c)…
it is possible to shoot an arrow at a speed as high as 166 ,how long would the arrow be in the air
consider a 1200kg car cruising steadily on a level road
A 54-kg ice skater pushes off the wall of the rink, giving herself an initial speed of 2.5 m/s . She then coasts with no further effort. The frictional coefficient between skates and ice is 0.025. How far does she go?
1. A square beam made using concrete with f'c = 6000 psi and steel with fy = 60000 psi has a width b = 20 in., an effective depth d = 17.5 in., and a total depth h = 20 in. The concrete tensile strength in bending (modulus of rupture) is fr = 530 psi. The elastic modulus of concrete and steel…
Data for one stage of the 2004 Tour de France show that Lance Armstrong’s average speed was 15 m/s, and that keeping Lance and his bike moving at this zippy pace required a power of 450 W. What was the average forward force keeping Lance and his bike moving forward? To put this in…
A typical human head has a mass of 5.0 kg. If the head is moving at some speed and strikes a fixed surface, it will come to rest. A helmet can help protect against injury; the foam in the helmet allows the head to come to rest over a longer distance, reducing the force on the head. The foam…
In a typical tee shot, a golf ball is hit by the 300 g head of a club moving at a speed of 40 m/s. The collision with the ball happens so fast that the collision can be treated as the collision of a 300 g mass with a stationary ball—the shaft of the club and the golfer can be ignored. The…
The electric force of repulsion between two electrons is similar to the gravitational force [ Fe=k(q1q2/r^2) ], where k is called Planck’s constant, q is the charge on a particle, and r is the distance separating the charges. Don’t look up the value of k. We’re not looking for an exact…
Spring into action A locust can jump as far as 1 meter, an impressive distance for such a small animal. To make such a jump, its legs must extend much more rapidly than muscles can ordinarily contract. Thus, instead of using its muscles to make the jump directly, the locust uses them to…
A 2.0 g desert locust can achieve a takeoff speed of 3.6 m/s (comparable to the best human jumpers) by using energy stored in an internal “spring” near the knee joint. When the locust jumps, what energy transformation takes place? What is the minimum amount of energy stored in the…
A 200 g block on a frictionless surface is pushed against a spring with spring constant 500 N/m, compressing the spring by 2.0 cm. When the block is released, at what speed does it shoot away from the spring?
A car sits at rest at the top of a hill. A small push sends it rolling down a hill. After its height has dropped by 5.0 m, it is moving at a good clip. Write down the equation for conservation of energy, noting the choice of system, the initial and final states, and what energy…
When you run a heat engine, some (or most) of the energy is “wasted” as heat transferred to the cold reservoir. Suppose someone suggests making a 100% efficient heat engine by using some of the output of the heat engine to run a heat pump to transfer this heat back to the hot reservoir.…
A typical gasoline-powered car stops by braking. Friction in the brakes brings the car to rest by transforming kinetic energy to thermal energy. Electric vehicles often stop by using regenerative braking, with the engine used as a generator, transforming the kinetic energy of the vehicle…
At The Geysers geothermal power plant in northern California, electricity is generated by using the temperature difference between the 15 °C surface and 240 °C rock deep underground. What is the maximum possible efficiency? What happens to the energy that is extracted from the steam that is…
A container holds 4.0 x 1022 molecules of an ideal gas at 0 °C. A piston compresses the gas, doing 30 J of work. At the end of the compression, the gas temperature has increased to 10 °C. During this process, how much heat is transferred to or from the environment?
The air in a typical bedroom consists of about 8.0 x 1026 atoms. Suppose a small fan is running, using 50 W. And suppose that there is no other transfer of energy, as work or heat, into or out of, the air in the room. By how much does the temperature of the room increase during 10 minutes…
Using a fan to move air in a room will make you feel cooler, but it will actually warm up the room air. A small desk fan uses 50 W of electricity; all of this energy ends up as thermal energy in the air of the room in which it operates.
How far could a 68 kg person cycle at 15 km/hr on the energy in one slice of pizza? How far could she walk, at 5 km/hr? How far could she run, at 15 km/hr? Do you notice any trends in the distance values that you’ve calculated? Chemical energy from food is used for each of these activities.…
A 75 kg person climbs the 248 steps to the top of the Cape Hatteras lighthouse, a total climb of 59 m. How many Calories does he burn?
A person lifts a 20 kg box from the ground to a height of 1.0 m. A metabolic measurement shows that in doing this work her body uses 780 J of energy. What is her efficiency?
Light bulbs are rated by the power that they consume, not the light that they emit. A 100 W incandescent bulb emits approximately 4 W of visible light. What is the efficiency of the bulb?
Why can you not hear your distant neighbor's conversations in the winter?
Explain how you can lower the pitch of a note on a guitar by changing the string's length. If desired play a lower note, what would you do to the tension?
Enumerate various scenarios/cases of non-uniform stress distribution in solids. Explain with the help of examples why simple stress definition cannot be used in such cases.
A body having a mass of 20 kg rests on a surface inclined 30° to the horizontal. Assume a coefficient of friction of 0.76 and calculate the magnitude of the force F, acting at an angle of 40° with the inclined surface required to: a) Pull the body upwards; b) Pull the body downwards; c)…
it is possible to shoot an arrow at a speed as high as 166 ,how long would the arrow be in the air
consider a 1200kg car cruising steadily on a level road
A 54-kg ice skater pushes off the wall of the rink, giving herself an initial speed of 2.5 m/s . She then coasts with no further effort. The frictional coefficient between skates and ice is 0.025. How far does she go?
1. A square beam made using concrete with f'c = 6000 psi and steel with fy = 60000 psi has a width b = 20 in., an effective depth d = 17.5 in., and a total depth h = 20 in. The concrete tensile strength in bending (modulus of rupture) is fr = 530 psi. The elastic modulus of concrete and steel…