Physics Answers

You are on the second story of a building, using a rope to lower a box to your friend on the ground.

The box is moving downward at a constant velocity. Consider your system to be the box+rope. Is

the work done by you on the system positive, negative, or zero?

a three resistors of 4ohms, 12 ohms and 5 ohms are connected in parallel. if total current is 12A, find the current through each resistor

A stone has a mass of 5kg. If it takes the stone 4 sec to fall freely to the ground, calculate it's initial height above the ground, and the force with which the stone hit the ground.

A 400.0-N sign hangs from the end of a uniform strut. The strut is 4.0 m long and

weighs 600.0 N. The strut is supported by a hinge at the wall and by a cable whose

other end is tied to the wall at a point 3.0 m above the left end of the strut. Find the

tension in the supporting cable and the force of the hinge on the strut.

A 50-kg person stands 1.5 m away from one end of a uniform 6.0-m-long scaffold of mass 70.0 kg. Find the tensions in the two vertical ropes supporting the scaffold.

The mass of the meter stick is 150.0 g and the masses to the left of the fulcrum are m1=50.0gm1=50.0g and m2=75.0g.m2=75.0g. Find the mass m3m3 that balances

the system when it is attached at the right end of the stick, and the normal reaction force at the fulcrum when the system is balanced.

The nose of an ultralight plane is pointed south, and its airspeed indicator shows 35 m/s. The plane is in a 10-m/s wind blowing toward the southwest relative to the earth. (a) In a vector addition diagram, show the relationship of →vP/E (the velocity of the plane relative to the earth) to the two given vectors. (b) Letting x be east and y be north, find the components of →vP/E. (c) Find the magnitude and direction of →vP/E.

A river flows due south with a speed of 2.0 m/s. A man steers a motorboat across the river; his velocity relative to the water is 4.2 m/s due east. The river is 800 m wide. (a) What is his velocity (magnitude and direction) relative to the earth? (b) How much time is required to cross the river? (c) How far south of his starting point will he reach the opposite bank?

A Ferris wheel with radius 14.0 m is turning about a horizontal axis through its center. The linear speed of a passenger on the rim is constant and equal to 7.00 m/s. What are the magnitude and direction of the passenger’s acceleration as she passes through (a) the lowest point in her circular motion? (b) The highest point in her circular motion? (c) How much time does it take the Ferris wheel to make one revolution?

World-class sprinters can accelerate out of the starting blocks with an acceleration that is nearly horizontal and has magnitude 15 m/s². How much horizontal force must a 55-kg sprinter exert on the starting blocks during a start to produce this acceleration? Which body exerts the force that propels the sprinter: the blocks or the sprinter herself?