Physics Answers

A waterfall is 30 meters high, and 10000 kg of water flows over it per second. How much power does this flow generate? If all this power is converted to electricity, how many 100-watt bulb can it supply?

Each of the four engines of a DC airplane develops 7500 horse power when the cruising speed is 240 m/s. How much thrust does each engine produce under these circumstances?

A 15-kilowatt motor is used to hoist an 800 kg bucket of concrete to the twentieth floor of a building under construction to height of 90 m. assuming no energy is lost along the process, how much time is required?

The sun exerts a force of 4 X 10²⁸ N on Earth, and the Earth travels 9.4 x 10¹¹m in its annual orbit around the sun. How much work does the sun does on Earth in the course of one the year?

You need to use your cell phone, which broadcasts a signal at 900MHz

900MHz, but you are in an alley between two large buildings that have only a 5.0m

5.0m spacing between them. What is the angular width, in degrees, of the signal after it emerges from between the buildings?

A boy ties a rope to a 30 kg object, as shown below. He pulls on the rope with a force of 150 N. The rope makes an angle of 20 degrees with the horizontal. The coefficient of friction between the object and surface is .12. Assume that the surface is horizontal and flat.

a.     Draw a free body diagram for the object.

b.     Calculate the weight of the object.

c.     Calculate the x and y components of the tension in the rope.

d.     Calculate the normal force acting on the object.

e.     Calculate the acceleration of the object.

10. A small child is eating dinner on a flat table that is 1 meter tall. When asked to eat his vegetables, the child pushes his plate away from him at a speed of 4 m/s. Due to friction, the plate decelerates at a constant rate of 1 m/s2. After 1 second, the plate falls off the edge of the table.

a.     How far did the plate travel over the 1 second?

b.     What is the speed of the plate at the instant it falls off the table?

c.     How much time will pass between the instant the plate leaves the table and the instant it reaches the ground?

d.     At what speed will the plate strike the ground?

e.     At what angle will the plate strike the ground?

1.     How much force is needed to accelerate a 66 kg skier at 2 m/sec²? (132N)

A sample of liquid gold is cooled and allowed to solidify. Calculate the amount of energy in cooling a 0.5kg sample of this gold from 1100 degrees Celsius to 25 degrees Celsius. The melting point of gold is 1063 degrees Celsius, the latent heat of fusion for gold is 65kJ/kg and the specific heat capacity of gold is 130 J/kg ºC. Does this process absorb or release energy? Make a sketch of a temperature-time graph for the reaction.

 a man who with 55kg, on a skateboard. He had an

initial speed of 2.77m/s when descending the stairs at a height of 2m.

Calculate the man’s potential energy when his speed is 6m/s