Exam 2

A child of mass m rides on a Ferris wheel as shown in the figure. The child moves in a vertical circle of radius 10.0 m at a constant speed of 10.00 m/s. Determine the force exerted by the seat on the child at the bottom of the ride. Express your answer in terms of the weight of the child, mg.

-0.020 mg - child loses contact with seat

A 2 kg block situated on a rough incline is connected to a light spring having a force constant of 100 N/m. See figure below. The block is released from rest when the spring is unstretched. The pulley is frictionless. The block moves down the incline 20 cm before coming to rest. What is the coefficient of friction between the block and the incline?

.115

A 200-g block is released from rest at point A along the diameter of the inside of the smooth semi-spherical bowl of radius = 30 cm shown in the figure below. What is its kinetic energy at point C? Make sure you convert units!!! SHOW YOUR WORK!

.196 J

A 20-kg block is connected to tr 30-kg block by a string that passes over a frictionless pulley. The 30-kg block is connected to a spring of negligible mass with a force constant 250 N/m as in the figure below. The spring is unstretched as shown in the figure, and the incline is smooth. The 20-kg block is pulled a distance of 20 cm down the incline so that the 30-kg block is 40 cm above the floor and is then released from rest. Find the speed of each block when the 30-kg block is 20 cm above the floor (that is when the string is unstretched).

1.24 m/s

A puck of mass 0.500 kg is attached to the end of a cord 1.50 m long. The puck moves in a horizontal circle as shown in the figure. If the cord can withstand a maximum tension of 50.0 N, what is the maximum speed at which the puck can move before the cord breaks? Assume the string remains horizontal during the motion.

12.2 m/s

In a ballistic pendulum experiment suppose that h = 5 cm, m1 = 5 g, and m2 = 1 kg. Find the initial speed of the projectile/bullet. The block is m2 and the bullet is m1. SHOW YOUR WORK

199 m/s

A 6.0-kg block initially at rest is pulled to the right along a frictionless, horizontal surface by a constant horizontal force of magnitude 12 N. Find the block's speed after it has moved through a horizontal distance of 3.0 m. Use W = Δ𝐾

3.5 m/s

A rocket moving in free space has a speed of 3 x 103 m/s. Its engines are turned on and its fuel is ejected at 5 x 103 m/s opposite to the rockets direction and relative to the rocket. What is the thrust on the rocket if it burns fuel at the rate of 50 kg/s?

2.50 x 105 N

A railroad tank car weighing 300,000 N is coasting along a level track with negligible friction at 20 km/hr. The car has a leak in the bottom. What is the speed of the car when it has lost 5000 N?

20 km/hr

A 3.00 kg block slides down a curved ramp as shown below. The work done by friction as the block slides from point A to B is 25 J. If the block starts from rest at point A what is the speed of the block when it reaches point B. The height of the curved ramp is 2.00 m.

4.75 m/s

An elevator car has a mass of 1600 kg and is carrying passengers having a combined mass of 200 kg. A constant friction force of 4000 N retards its motion. How much power must a motor deliver to lift the elevator car and its passengers at a constant speed of 3.00 m/s?

6.49 x 104 W

A single conservative force Fx = (2x + 4) N acts on a 5-kg particle, where x is in meters. As the particle moves along the x axis from x = 1 m to x = 5 m, calculate is kinetic energy x at x = 5 m if its speed is at x = 1 m is 3 m/s.

62.5 J

The gravitational potential energy of a system

Can be positive or negative

The work done by a conservative force is path dependent

False

Suppose the puck in question 2 moves in a circle of larger radius at the same speed v. Is the cord more likely or less likely to break?

Less likely

You are traveling along a freeway at 65 mi/h. Your car has kinetic energy. You suddenly skid to a stop because of congestion in traffic. Where is the kinetic energy your car once had?

Some of it has transformed to internal energy and some of it transferred away by mechanical waves.

When work is done on a system and the only change in the system is in the speed of its members, the net work done on the system equals the change in kinetic energy of the system: 𝑊=Δ𝐾

True

You are riding on a Ferris wheel that is rotating with constant speed. The car in which you are riding always maintains its correct upward orientation; it does not invert. What is the direction of the normal force on you from the seat when you are at the top of the wheel

Upward

The gravitational force exerted by the Sun on the Earth holds the Earth in an orbit around the Sun. Let us assume that the orbit is perfectly circular. The work done by this gravitational force during a short time interval in which the Earth moves through a displacement in its orbital path is

Zero

A ball is connected to a light spring suspended vertically. When pulled downward from its equilibrium position and released, the ball oscillates up and down. In the system of the ball and the spring, and the Earth what forms of energy are there during the motion?

kinetic, elastic potential, and gravitational potential

Four masses are placed on the corners of uniform square board whose sides are 3.0 m long. The board has a mass of 10 kg. The masses are distributed as follows: 0.1 kg at A, 0.5 kg at B, 0.09 kg at C, and 0.01 kg at D. Find the center of mass of the system.

ycm = 1.43 m and xcm = 1.56 m