Physics 2 Online Quiz 1: Dynamics

Explanation
In option a, the ship is moving at a constant speed of 10 knots in a straight path. In option d, the bus is moving at a constant speed of 40 km/h around a curve. Therefore, the bodies that move with constant speed are a and d only.

Explanation
A ship moving at 10 knots in a straight path will have a constant velocity because both the speed and direction remain unchanged. Velocity is defined as the rate of change of displacement, and since the ship is moving in a straight line at a constant speed, there is no change in displacement over time. Therefore, the ship is moving with constant velocity.

Explanation
In physics, acceleration is defined as the rate of change of velocity. Velocity is a vector quantity that includes both magnitude and direction. In case a, the ship is moving at a constant speed in a straight path, so there is no change in velocity and therefore no acceleration. However, in case b, the car is initially moving at a certain speed and then slows down to stop, indicating a change in velocity and hence acceleration. In case c, the storm initially moves northeast and then changes its direction to move eastward, indicating a change in velocity and acceleration. In case d, the bus is moving at a constant speed but around a curve, which means it is changing its direction and hence experiencing acceleration. Therefore, the bodies that are accelerating are b, c, and d only.

Explanation
Since the car is traveling at a constant speed of 20 m/s, its speed remains the same after 4 seconds. Therefore, the correct answer is 20 m/s.

Explanation
The force of friction between the tires and the road is equal to 40 N because the boys are applying a force of 20 N each, resulting in a total force of 40 N. Since the jeep does not move, it means that the force of friction is equal to the total force applied by the boys.

Explanation
As an object freely falls, its velocity increases. This is because the object is accelerating due to the force of gravity. As it falls, the force of gravity pulls it downwards, causing it to gain speed and its velocity to increase.

Explanation
While a car travels around a circular track at a constant speed, its acceleration is not zero because it is constantly changing direction, which requires centripetal acceleration. Additionally, its speed is also not zero because it is moving along the track at a constant speed. Therefore, the correct answer is neither a nor b.

Explanation
The force of friction on a sliding object is equal to the applied force needed to maintain a constant velocity. In this case, the force of friction is 10 N, so the applied force needed to maintain a constant velocity is also 10 N.

Explanation
The correct answer is "at the same time as the light block". This is because neglecting friction means that both blocks will experience the same acceleration down the inclined plane. Since they start sliding together, they will continue to maintain the same relative positions throughout the motion. Therefore, they will reach the bottom of the inclined plane at the same time.

Explanation
The force of friction between the block and the surface is 6 N. This is because if the block is being dragged without acceleration, it means that the force of friction is equal in magnitude and opposite in direction to the applied force of 6 N. Therefore, the force of friction must also be 6 N.

Explanation
The frictional force between two surfaces in contact does not depend on the areas of the surfaces. Friction is determined by the normal force pressing one surface against the other, whether the surfaces are stationary or in relative motion, and whether or not a lubricant is used. The size or shape of the surfaces does not affect the frictional force.

Explanation
In the given diagram (a), there are four forces acting on box m. These forces include the gravitational force pulling the box downwards, the normal force exerted by the surface on the box in the upward direction, the frictional force opposing the motion of the box, and the applied force pushing the box in a certain direction.

Explanation
In diagram (a), there are four forces acting on box M. The weight of the box is acting downwards due to gravity. The normal force is acting upwards perpendicular to the surface the box is resting on. The friction force is acting in the opposite direction to the motion or potential motion of the box. Finally, there is a force being applied to the box, which could be from pushing or pulling it. Therefore, there are four forces acting on box M in diagram (a).

Explanation
In the given diagram (a), there are two boxes. Each box is in contact with the ground, so there is a normal force acting on each box due to the weight of the box. Additionally, there is a frictional force acting on each box due to the presence of friction on all surfaces. Therefore, for each box, there are two forces acting vertically (normal force and weight) and two forces acting horizontally (frictional force and weight). Since there are two boxes, the total number of forces acting on the two boxes is 8.

Explanation
In diagram (b), there are two boxes in contact with each other. Each box experiences its weight force acting downwards and an equal and opposite normal force acting upwards from the surface it is resting on. Additionally, there is a friction force acting between the two boxes in the opposite direction of their relative motion. Therefore, there are a total of 10 forces acting on the two boxes in diagram (b).