Energy and Work
A force, F, is applied to an object with a displacement, Δd. When does the equation W 5 FΔd equal the work done by the force on the object?
(a) always
(b) when the force is in the same direction as the displacement
(c) when the force is perpendicular to the displacement
(d) when the force is at an angle of 45 degrees to the displacement
(b) when the force is in the same direction as the displacement
As you increase the mass attached to the spring (similar to Part A in the energy springs lab), what happens to the force and stretch of the spring? Is the force constant as the masses increase?
As the masses increase, the force increases and the stretch increases (force is linearly proportional to stretch, for a constant spring force). The force is NOT constant as the masses increase (it is changing) and thus the stretch is changing.
Suppose two billiard balls, A and B, with the same mass undergo a head-on 100% elastic collision. Ball A was initially stationary. After the collision, which statement is true?
(a) One ball is moving and one is stationary.
(b) Both balls are moving.
(c) Both balls are stationary.
(d) All of the above outcomes are possible.
(a) One ball is moving and one is stationary.
A cellphone has a rest energy of 2.25 x 1016 J. Calculate its rest mass.
0.25 kg
A mover pushes a sofa across the floor of a van. The mover applies 475 N of horizontal force to the sofa and pushes it 1.2 m. What is the work done on the sofa by the mover?
570 J
If a mass of 0.65 kg attached to a vertical spring stretches the spring 4.0 cm from its original equilibrium position, what is the spring constant?
(a) 0.27 N/m
(b) 16 N/m
(c) 60 N/m
(d) 160 N/m
(d) 160 N/m
A ball with a mass of 0.5 kg, initially at rest, is struck with a bat and acquires a velocity of 4.0 m/s. What is the magnitude of the change in momentum of the ball?
2.0 kgm/s
A mass, m, has rest energy Erest. If the mass is accelerated to 0.75c, what is its energy in terms of Erest?
(1.51)Erest
Two identical marbles are dropped in a classroom. Marble A is dropped from 1.00 m, and marble B is dropped from 0.50 m. Compare the kinetic energies of the two marbles just before they strike the ground.
(a) Marble A has the same kinetic energy as marble B.
(b) Marble A has 1.4 times as much kinetic energy as marble B.
(c) Marble A has 2.0 times as much kinetic energy as marble B.
(d) Marble A has 4.0 times as much kinetic energy as marble B.
(c) Marble A has 2.0 times as much kinetic energy as marble B.
A spring is compressed and then released to launch a ball vertically upward. Ignoring the small change in Eg as the spring decompresses, explain what is happening (in terms of energy, work, and forces) when the ball starts from rest (when spring is compressed) and travels to a maximum height?
When the ball is at rest, the ball has no kinetic or gravitational potential energy, while the spring has all elastic potential energy due to the compression of the spring. When the spring decompresses, it exerts an elastic force on the ball causing it to travel vertically upward. This force exerts work on the ball. Once travelling upward, the ball gains kinetic and gravitational potential energy. Once the ball reaches max height, it has all gravitational potential energy.
A 2200 kg car starts from rest and speeds up to 12 m/s in 5.2 s. What is the net force acting on the car?
5.1 × 103 N
Particle X undergoes fusion with particle Y and combine to form particle Z and a neutron. If there is also some light energy released during the reaction, which statement correctly compares the masses of all three particles?
(a) The sum of the masses of particle Z and the neutron is the same as the sum of the masses of particles X and Y.
(b) The sum of the masses of particle Z and the neutron is greater than the sum of particles X and Y.
(c) The sum of the masses of particle Z and the neutron is lesser than the sum of particles X and Y.
(d) The masses of all three particles are equal.
(c) The sum of the masses of particle Z and the neutron is lesser than the sum of particles X and Y.