Physics Summative Test

A uniform beam balances at its midpoint. If a 20 N weight is hung 2.0 m from the pivot, where must a 40 N weight be hung to maintain equilibrium?

• 0.5 m

• 1.0 m

• 2.0 m

• 4.0 m

A gymnast pulls her arms inward during a spin. What happens to her angular speed, and why?

• It increases because moment of inertia decreases

• It decreases because moment of inertia increases

• It stays the same because angular momentum is not conserved

• It becomes zero because torque cancels rotation

A solid disk and a hollow cylinder (same mass and radius) roll without slipping from rest down the same incline. Which reaches the bottom first and why?

• Disk, because it has a smaller moment of inertia

• Cylinder, because it has a larger moment of inertia

• Both at the same time because masses are equal

• Cylinder, because it has greater surface contact

Engineers design a flywheel to store rotational energy for an engine. For a given angular speed, which design change stores more energy?

• Increase the flywheel's radius while keeping mass distribution near rim

• Decrease the flywheel's mass

• Concentrate mass at the center

• Increase friction

A ladder of length L leans against a smooth (frictionless) wall making an angle θ with the horizontal. Which force provides the horizontal balance that prevents slipping?

• Friction at the ground

• Normal reaction at the ground

• Normal reaction at the wall

• Weight of the ladder

Scientists consider a hypothetical “Super-Earth” with the same mass as Earth but double the radius. Predict how the surface gravity compares to Earth’s.

• People would weigh the same as on Earth

• Objects would fall with only one-fourth Earth’s acceleration

• Satellites in low orbit would move faster than on Earth

• Mountain heights would increase due to stronger gravity

Astronauts in the International Space Station feel weightless because:

• they are in a continuous state of free fall around the Earth.

• there is no gravity in space.

• the space station is far from Earth's gravitational pull.

• they are moving away from the Earth at high speed.

A) There is negligible gravity at orbit altitude B) Both astronauts and station are in free fall around Earth C) Their mass is reduced in orbit D) Earth's gravity is canceled by centrifugal force

• There is negligible gravity at orbit altitude

• Both astronauts and station are in free fall around Earth

• Their mass is reduced in orbit

• Earth's gravity is canceled by centrifugal force

A satellite orbits Earth at radius R with orbital period T. If the orbit radius is increased to 2R, what happens to the orbital period (Kepler’s third law)?

• Period becomes 2T

• Period becomes 2√2 · T

• Period becomes 4T

• Period becomes √2 · T

Two spherical planets have equal mass but Planet A has smaller radius than Planet B. Which planet has greater surface gravity and why?

• Planet A, because surface is closer to mass center

• Planet B, because larger radius increases gravity

• Both same because masses are equal

• Cannot be determined without density