SIFT Physics and Simple Machines 4

Question 1

Power is defined as:

Accepted Answer

The rate at which work is done

Answer

Power = Work / Time, measuring how quickly energy is transferred or work is done, expressed in watts (W).

Question 2

An object at rest remains at rest unless acted upon by an unbalanced force. This describes:

Accepted Answer

Newton's First Law (inertia)

Answer

Newton's First Law, also called the law of inertia, states that objects resist changes in their state of motion.

Question 3

A block-and-tackle system uses 5 rope segments to support a load. What is its ideal mechanical advantage?

Accepted Answer

5

Answer

In a block-and-tackle system, the ideal MA equals the number of rope segments supporting the load, which is 5.

Question 4

When a ball is thrown upward, its kinetic energy at the peak of its trajectory is:

Accepted Answer

Zero

Answer

At the peak, the ball momentarily stops (velocity = 0), so kinetic energy (½mv²) equals zero; all energy has converted to potential energy.

Question 5

The efficiency of a machine is defined as:

Accepted Answer

(Useful work output / Work input) × 100%

Answer

Efficiency measures what fraction of input energy does useful work, always less than 100% due to friction and other losses.

SIFT Exam Practice Test