Answer:
The correct answer are A and D.
Explanation:
According to the Newton's second law of motion, Acceleration on an object is directly proportional to the net force acting on it. It means that when we introduce force, it introduce acceleration on an object. When an object has constant acceleration, then there must be constant force acting on it. Thus a constant acceleration is required constant force act on it.
A.) Gravitational acceleration is considered constant near the Earth's surface. So, It has constant motion.
B.) The force of a toy car on each looped section of the track has not only the gravitational force, but also the centripetal force. The centripetal acceleration at the top of the loop is different from the centripetal acceleration at the bottom of the loop, so the motion of the toy car along the track is not constant.
C.) The rocket is supported by a water-propelled arm. The forces on the rocket are therefore the water-propelled force and the gravitation. When rocket moves upward, velocity decreases and when rocket moves downward velocity increases. Direction of rocket changes and hence acceleration. Therefore, the acceleration of the rocket is not constant.
D.)The cart is subjected to constant force i.e force of gravity and/or frictional force of the cart by the incline so that the acceleration is steady.
So, Correct answer are A and D.
