General Science GK Questions with Answers – Page 121

The erg is the unit of work in the CGS system, being one dyne of force acting through one centimetre, and since one newton is one lakh dyne and one metre is a hundred centimetre, one joule works out to ten million erg, that is 10 raised to the power…

A stone at rest at a height has no motion and therefore no kinetic energy, but it possesses gravitational potential energy equal to its mass into the acceleration due to gravity into the height of the tower.

The force he applies to support the load acts vertically upward, while his displacement along the platform is horizontal, so the angle between force and displacement is ninety degrees and the work done against gravity is zero, however tired he may feel.

The work-energy theorem states that the net work done on a body equals the difference between its final and initial kinetic energies, which is why a push that speeds a body up does positive work while friction, which slows it, does negative work.

A dynamo, also called a generator, is turned by some mechanical agency such as falling water, steam or a bicycle wheel, and the rotation of a coil in a magnetic field produces an electric current by electromagnetic induction.

Kinetic energy is half the mass into the square of the speed, so when the speed is multiplied by two the energy is multiplied by two squared, that is four.

Household electricity is billed in these units, and one kilowatt hour, popularly called one unit, is the energy consumed when an appliance of one kilowatt runs for one hour; in SI terms it equals 3.6 million joule.

The horsepower is an older unit of power that survives in the rating of motors and vehicles, and one horsepower is taken as about 746 watt, that is roughly three quarters of a kilowatt.

Power is the rate of doing work, that is work divided by the time taken, so its unit is the joule per second, which is named the watt after James Watt.

Kinetic energy is the energy a body has because of its motion, and it grows with the square of the speed, so a body moving twice as fast carries four times the kinetic energy.

Work equals force into displacement into the cosine of the angle between them, and the cosine of ninety degrees is zero, so a force at right angles to the motion does no work at all.

Work is the product of force and displacement, so its unit is the newton metre, which is given the name joule; one joule of work is done when a force of one newton moves a body through one metre in its own direction.

Whether the hands are moved or not, the momentum of the ball must be brought down to zero.

Inertia is the tendency of a body to resist any change in its state of rest or of uniform motion, and the heavier the body the harder it is to start or to stop.

The slope of any graph is the change on the vertical axis divided by the change on the horizontal axis; here that is distance divided by time, which is speed by definition.

The third law says that to every action there is an equal and opposite reaction, and the crucial point is that the two forces act on two different bodies.

On a velocity-time graph the height of the curve is velocity and the base is time, so the area enclosed is velocity multiplied by time, which is displacement.

The three equations of uniformly accelerated motion are v equals u plus at, s equals ut plus half of a t squared, and v squared equals u squared plus twice a s, where u is the initial velocity, v the final velocity, a the acceleration, t the time and s…

While the bus is moving, the passenger's whole body moves with it. When the brakes are applied, the feet stop along with the floor of the bus, but the upper body tends to keep moving forward at the same speed, and the passenger is thrown forward.

Momentum is the product of mass and velocity, so its unit is the unit of mass multiplied by the unit of velocity, that is kilogram multiplied by metre per second.