Work and energy — Important Questions

Kinetic energy

Step 1: Energy is the ability to do work, and moving objects can do work on other objects. Step 2: When a cricket ball hits the stumps, it does work because of its motion. Step 3: The energy due to motion is specifically called kinetic energy (from Greek word 'kinesis' meaning motion). Step 4: Potential energy is due to position or shape, heat energy is thermal energy, chemical energy is stored in bonds. Step 5: Only kinetic energy is directly related to the motion of objects.

Both mass and velocity

Step 1: Kinetic energy formula is KE = ½mv², where m is mass and v is velocity. Step 2: The formula shows that KE depends on both mass (m) and velocity (v). Step 3: A heavier object moving at same speed has more kinetic energy than lighter object. Step 4: Similarly, faster moving object has more kinetic energy than slower one with same mass. Step 5: Height above ground affects potential energy, not kinetic energy.

Only potential energy

Step 1: The book is at rest on the shelf, so it has no motion and therefore no kinetic energy. Step 2: However, the book is at a height above the ground level. Step 3: Due to this height, it has gravitational potential energy (PE = mgh). Step 4: If the book falls, this potential energy converts to kinetic energy. Step 5: At rest and at height, objects have only potential energy, not kinetic energy.

PE = mgh

Step 1: Gravitational potential energy is the energy stored due to height above ground. Step 2: To lift an object of mass m to height h, work done against gravity = force × distance = mg × h. Step 3: This work gets stored as potential energy, so PE = mgh. Step 4: ½mv² is kinetic energy formula, Fs is work formula, P/t doesn't represent any energy. Step 5: Only mgh correctly represents energy due to gravitational position.