Physics: Motion, Energy, and Forces

Inertia is the property of matter that causes a moving body to resist changes in its state of motion. It is directly proportional to mass - larger objects have more inertia. Velocity, acceleration, and displacement describe motion but don't explain resistance to change.

Using impulse-momentum theorem: impulse J = F × t = Δp = mΔv. When force doubles (2F) and time doubles (2t), impulse becomes 2F × 2t = 4Ft, which is 4 times the original. Since mass is constant, velocity change also increases 4-fold. The 8-fold option incorrectly multiplies only the force, while 2-fold ignores one factor.

Kinetic energy is given by KE = 1/2 mv², where m is mass and v is velocity. Temperature and entropy relate to thermodynamics, not mechanics. Height and mass determine potential energy (PE = mgh), not kinetic energy.

Net force = applied force - friction. Friction = μmg = 0.4 × 10 × 9.8 = 39.2N. Applied force = 20N, so friction exceeds applied force. The object won't move, meaning acceleration is 0 m/s². Options B and D come from incorrectly ignoring friction or misapplying the formula.

Concave lenses always diverge light and cannot form real images. Convex mirrors also diverge light, producing only virtual images. Both concave and convex lenses can form real images depending on object position, and concave mirrors can form real images when the object is beyond the focal point.

Orbiting spacecraft are in continuous free fall toward Earth, but their forward velocity prevents them from hitting the ground - they keep missing it as they fall. This creates the apparent weightlessness. Microgravity is the result, not the cause. Frictionless glide is incorrect in atmosphere; counter thrust is meaningless.

Speed is distance per time (scalar), while velocity is displacement per time (vector). Similarly, distance is a scalar quantity measuring path length, while displacement is a vector measuring straight-line change in position. The analogy holds: scalar : vector :: scalar : vector. The other options are unrelated concepts.

Work is defined as force multiplied by displacement in the direction of the force. Since the carpenter holds the drywall stationary, there is no displacement, so the work done is zero joules. The time spent holding and the weight of the object don't matter when nothing moves.

Both vehicles have the same momentum: p = mv = 1000 × 40 = 40,000 kg·m/s for the VW and p = 4000 × 10 = 40,000 kg·m/s for the Explorer. However, kinetic energy depends on velocity squared (KE = 1/2 mv²). The VW has 800,000 J while the Explorer has only 200,000 J, so the VW has much more kinetic energy despite equal momentum.

The pendulum bob's speed at the bottom is given by v = sqrt(2gh). When the height is quadrupled, the speed only doubles (sqrt(4) = 2). In a perfectly elastic collision between objects of equal mass, the bob transfers all its velocity to the block, so the block's initial speed becomes twice as fast.