Test: Forces and Energy - Year 8 MCQ

Balanced forces are equal in size and opposite in direction, resulting in a net force of zero. According to Newton’s First Law, an object with no net force will either remain at rest or continue moving at a constant speed in a straight line. Options A, B, and D describe scenarios with unbalanced forces.

Terminal velocity occurs when the upward air resistance equals the downward weight of the falling object, balancing the forces. This results in a constant speed with no further acceleration. The parachute does not increase weight, reduce atmospheric pressure, or cause indefinite speed increase, making options A, C, and D incorrect.

The change in direction occurs because the racket applies a greater force than the ball’s momentum, creating an unbalanced force that alters its path. The ball’s weight and air resistance are not primary factors, speed changes, and forces are unbalanced during the hit, making options B, C, and D incorrect.

Scientists use metres per second (m/s) as the standard unit for speed globally, as it aligns with the metric system. Miles per hour, kilometres per hour, and knots are used in specific contexts (e.g., road travel, aviation), but they are not the standard scientific unit, making options A, B, and D incorrect.

Speed is calculated as Speed = Distance ÷ Time. Here, 200 metres ÷ 40 seconds = 5 m/s. Option B (200 ÷ 25 = 8), option C (200 ÷ 20 = 10), and option D (200 ÷ 100 = 2) result from incorrect calculations or assumptions.

A horizontal line on a distance-time graph indicates that the distance remains constant while time progresses, meaning the object is stationary (speed = 0). A straight upward line represents constant speed, a curved line may indicate changing speed, and a downward line shows movement back toward the starting point, making options A, B, and D incorrect.

The moment of a force is calculated as Moment = Force (in newtons) × Distance (in metres), resulting in the unit newton metre (Nm). Newton is a unit of force, metre is a unit of distance, and newton per metre is not used for moments, making options A, B, and D incorrect.

Pressure is calculated as Pressure = Force ÷ Area. A sharp knife has a smaller contact area, which increases pressure for the same force, making cutting easier. Increasing force also raises pressure but is not the primary role of sharpness, and increasing area reduces pressure, making options A, C, and D incorrect.

Pressure in liquids increases with depth due to the weight of the liquid above. The dam’s base is wider to provide greater structural strength to resist the higher water pressure at the bottom. It does not reduce flow, affect atmospheric pressure, or balance weight in this context, making options A, C, and B incorrect.

Higher temperatures increase the speed of gas particles, accelerating diffusion as particles move faster from areas of high to low concentration. Lower temperatures slow diffusion, smaller concentration differences reduce the rate, and reduced particle movement is not a factor, making options A, B, and D incorrect.