Physics Answers

:An attractive force of 12kN is experienced by two charges of magnitude 4nC and 7nC. At what

distance must these two charges be to experience this force?

8. A ball rolls horizontally with a speed 0f 7.6 m/s off the edge of a tall platform. If the ball lands 8.7 m from the point on the ground directly below the edge of the platform, what is the height of the platform?

9. A stone thrown off a bridge 20 m above a river has an initial velocity of 12 m/s at an angle of 45° above the horizontal.

What is the range of the stone?

At what velocity does the stone strike the water?

26. A ball with a horizontal speed of 1 m/s rolls off a bench 2 m high.

How long will the ball take to reach the floor?

How far from a point on the floor directly below the edge of the bench will the ball land?

27. An electron is ejected horizontally at a speed of 1.5 X10⁶ m/s from the electron gun of a computer monitor. If the viewing screen is 35 cm from the end of the gun, how far will the electrons travel in the vertical direction before hitting the screen?

A young girl standing on a bridge throws a stone with an initial velocity of 12 m/s at a downward angle of 45° to the horizontal, in an attempt to hit a block of wood floating in the river below. If the stone is thrown from a height of 20 m and it just reaches the water when the block is 13 m from the bridge, does the stone hit the block?

Suppose a golf ball is hit off with the tee with an initial velocity of 30 m/s at an angle of 35° to the horizontal.

What is the maximum height reached by the ball?

What is its range?

a. An astronaut has a mass of 70 kg when measured on Earth. What is her weight in deep space, far from any celestial body? What is her mass there?

b. Here is a story of a horse and a farmer: One day, the farmer attaches a heavy cart to the horse and demands that the horse pull the cart. “Well,” says the horse, “I cannot pull the cart, because, according to Newton’s third law, if I apply a force to the cart, the cart will apply an equal and opposite force on me. The net result will be that I cannot pull the cart, since all the forces will cancel. Therefore, it is impossible for me to pull this cart.” The farmer was very upset! What could he say to persuade the horse to move?

Determine the frequency with which each value occurred and tabulate the data accordingly.

1. An object weighs 300 N on Earth and 50 N on the Moon. Does the object also have less inertia on the Moon?

2. Consider a child holding a helium balloon in a closed car at rest. What would the child observe when the car (a) accelerates from rest and (b) brakes to a stop? (The balloon does not touch the roof of the car.)

3. A traffic light weighing 1 X10² N hangs from a vertical cable tied to two other cables that are fastened to a support as shown in the figure. The upper cable makes angles of 37° and 53° with the horizontal. Find the tension in the three cables.

4. The distance between two telephone poles is 50 m. When a 1 kg bird lands on the telephone wire midway between the poles, the wire sags 0.2 m. Draw a free-body

diagram of the bird. How much tension does the bird produce in the wire? Ignore the weight of the wire.

1. a.) Suppose a hockey puck slides down a frictionless ramp with an acceleration of 5 m/s². What angle does the ramp make with respect to the horizontal?

b) If the ramp has a length of 6 m, how long does it take the puck to reach the bottom?

c) Now suppose the mass of the puck is doubled, What will be it’s acceleration?

2. A space-walking astronaut of total mass 148 kg exerts a force of 265 N on a free-floating satellite of mass 635 kg, pushing it in the +x direction.

a. What is the reaction force exerted by the satellite on the astronaut?

b. Calculate the acceleration of the astronaut

c.The acceleration of the satellite