Chapter 7 8 and 9 Practice Quiz

Object 1 is moving along the x-axis with an initial momentum such that p1xi = +16 kg·m/s and p1yi = 0. As the drawing shows, object 1 collides with object 2 which is initially at rest. After the collision, object 1 has a momentum whose y-component is p1yf = - 5 kg·m/s. What is the y-component of object 2?

+ 5 kg·m/s

Consider the force F directed as shown below. This force acts on an object that can move along either the x or y axis. Complete the following statement: The work done by F is positive when the displacement of the object is either along the ______ axis, or along the ______ axis.

- x, + y

In the graph shown below, m1 = m2, and the springs they are attached to are identical. However, the displacement from equilibrium of the spring attached to m1 is x1 but that of m2 is five times further x2 = 5x1. How does the work required to pull m2 compare with the work required to pull m1?

25 times greater.

By what factor does the kinetic energy of a car change when its speed is doubled?

4

Which one of the following systems listed below is an isolated system according to Conservation of Momentum. In all cases neglect friction.

A ball is dropped from the top of a building. The system is the ball and the Earth.

You are given 2 frictionless ramps and 2 identical blocks to slide down each of them. Both ramps have the same height h and the same length L, as shown below. You then release both blocks from rest at the height h. Which one of the following is TRUE regarding this situation when the blocks reach the bottom?

Both blocks have the same speed upon reaching the bottom.

Which one of the following is TRUE for an elastic collision between 2 objects that make up an isolated system?

Both the kinetic energy and the momentum of the system are conserved.

If you know the Impulse that has acted on an object of known mass m, you can calculate:

Its change in velocity.

A rock is thrown straight down from the top of a building. Which one of the following statements describes the energy transformation of the rock as it falls? Assume no air resistance

Its kinetic energy increases as its potential energy decreases.

Two isolated objects undergo a collision: mass m1 has a velocity v1i as it moves head-on towards mass m2 which is stationary. Is it possible for m1 to be at rest after the collision?

No

If only a single force acts on an object of mass m: (i) Does it necessarily change its kinetic energy?_______ , (ii) Does it necessarily change its velocity?________

No, Yes.

Two isolated objects undergo an inelastic collision: mass m1 has a velocity v1i as it moves head-on towards mass m2 which is stationary. Is it possible for both m1 and m2 to be at rest immediately after the collision?

No.

Two isolated objects undergo an inelastic collision: mass m1 > m2 and has a velocity v1i as it moves head-on towards mass m2 which is stationary. Is it possible for m1 to be at rest after the collision?

Only if v2f > v1i

Two hikers of identical weight decide to climb the same mountain and start from the same horizontal position. Sal chooses a steep trail, while Joe goes up via a gently sloped trail. When they each reach the top (same altitude), which one of the following is TRUE?

Sal has gained the same gravitational potential energy as Joe.

For which one of the following circumstances does the principle of conservation of mechanical energy apply (ΔK + ΔU = 0), even though there is a single non-conservative force acting on a moving object?

The non-conservative force is perpendicular to the displacement of the object.

Two identical stones are thrown with the same initial speed at the same instant from the level roof of a building at a height H above the ground. One stone is thrown at an angle of 30° above the horizontal, the other is thrown horizontally. Which one statement below is TRUE about the situation?

The stones strike the ground at different times but with the same speed.

Two forces F1 and F2 act on an object. As a result the speed of the object increases. Which one of the following must be FALSE? All others may be true.

The work done by both F1 and F2 is negative.

The gravitational force exerted by the Sun on the Earth keeps the Earth in orbit about the Sun. Assume the orbit is perfectly circular. What can be said about the work done by the gravitational force on the Earth as it moves through a displacement in its orbital path?

The work done is zero.

Two identical cars are traveling at the same speed; however, one is heading due East and the other due North. Which statement is TRUE regarding the kinetic energies K and momenta p of the cars?

They have the same K but different p.

A block at rest at the top of a ramp shaped in the form of a partial arc of a circle has a potential energy of mgh. The block is released from the top and slides down the rough ramp to the bottom as friction does work on it. Which one of the following is TRUE regarding this situation?

When the block reaches the bottom, its kinetic energy will be < mgh.

Which one of the following statements is FALSE?

in an inelastic collision, momentum is not conserved. in an elastic collision, kinetic energy is conserved.(T) in any collision (isolated system) momentum is conserved even when the kinetic energy is not.(T)

An object is falling through the atmosphere (ignore air resistance) and gains 20 J of kinetic energy. How is its gravitational potential energy affected?

its gravitational potential energy decreases by 20 J.

A single force acts on an object resulting in a reduction of the object's kinetic energy. Which one of the following is correct?

the angle between the force acting on the object and the objects displacement is > 90º.

A single forces acts on an object as the object is displaced in the same direction as the force. Which one is true in this situation.

the kinetic energy of the object increases.

If the total momentum of a system is changing:

the system must be under the influence a net impulse.