PHY 101 Mock Test 1

By definition, the normal force is the component of contact force perpendicular (normal) to the surface. Its magnitude depends on the situation.

The ball has the train’s initial horizontal velocity relative to the ground. Under gravity alone, it follows projectile motion (a parabola) as seen by the ground observer.

Newton’s second law for a system states that the net external force equals the total mass times the acceleration of the center of mass. Internal forces cancel in pairs.

This is the definition of a perfectly elastic collision.

v_AB = v_A – v_B = (60 N) – (80 N) = -20 N, which is 20 km/h in the opposite direction (South).

The center of mass of any system under the influence of a uniform gravitational field follows the simple parabolic trajectory of a point mass.

This is a common point of confusion. The two forces are an interaction pair between two different bodies, so they do not cancel for a single body.

The boat’s velocity relative to the shore is the vector sum of its velocity across the river and the river’s velocity downstream. With both constant, the resultant is constant, leading to straight-line motion at an angle.

With no horizontal force, the horizontal component of velocity remains unchanged. The vertical acceleration is always -g downward.

A · B = |A||B|cosθ. For θ = 90°, cos90° = 0, so the dot product is zero.

Mechanical energy (KE+PE) is constant if the work done by all non-conservative forces (like friction) is zero.

When vectors are opposite (180°), they subtract. The resultant magnitude is |A – B|, which is smaller than when they are at any other angle

Rotational KE = (1/2)Iω². KE is proportional to ω², so doubling ω increases KE by a factor of 2² = 4.

It does not exchange matter or energy with its surroundings.
Explanation: An isolated system has no interactions across its boundary, no transfer of mass, heat, or work.

Mechanical energy is lost to heat and sound (non-conservative forces). However, when considering all forms of energy, the total energy of the universe (ball + Earth + surroundings) is conserved.

A world line on a space-time plot shows an object’s position (space) at every moment (time).

With negligible external torque, L = Iω is constant. Decreasing I forces ω to increase to keep the product constant.

Impulse, J = ∫ F dt (or F_avg Δt for constant force), is a measure of the change in momentum it produces.

The first law introduces the property of matter known as inertia, which is the tendency of an object to resist changes in its state of motion.

Multiplying by a negative scalar (-2) scales the magnitude by 2 and reverses the direction by 180 degrees.