An object accelerates (changes its speed) only if the forces acting on it in one direction are greater than the forces in the opposite direction, All of the folloeing objects will accelerate EXCEPT
a)a ball striking a wall, in which the force of the ball on the wall is equal to the force of the wall on the ball
b) a gas balloon in which the buoyant force is greater than its weight and air resistance
c) a man in a parachute when the air resistance is less than his weight
d) a rocket fired straight up, when the engine thrust is equal to the air resistance
e) an airplane in horizontal flight when the thrust of the engine is equal to the drag of the air
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To determine which of the given objects will not accelerate, we need to consider Newton's second law of motion, which states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, this can be expressed as:
a = F_net / m
where:
a = acceleration
F_net = net force
m = mass of the object
Now, let's analyze each situation:
a) A ball striking a wall, in which the force of the ball on the wall is equal to the force of the wall on the ball.
In this scenario, the forces acting on the ball are balanced. Since the net force is zero (F_net = 0), according to Newton's second law, the ball will not accelerate.
b) A gas balloon in which the buoyant force is greater than its weight and air resistance.
In this case, there is an unbalanced force acting on the gas balloon. The buoyant force is greater than the combined weight and air resistance forces. Therefore, there is a net force, and the balloon will accelerate.
c) A man in a parachute when the air resistance is less than his weight.
Similar to the previous situation, the forces are unbalanced. In this case, the force of air resistance is less than the man's weight, which means there is a net force acting downward. The man with the parachute will accelerate downward.
d) A rocket fired straight up when the engine thrust is equal to the air resistance.
When the engine thrust is equal to the air resistance, the forces are balanced, resulting in a net force of zero. Thus, the rocket will not accelerate in the upward direction.
e) An airplane in horizontal flight when the thrust of the engine is equal to the drag of the air.
When the thrust of the engine is equal to the drag force, the forces are again balanced. This means there is no net force acting on the airplane, so it will not accelerate.
Based on the explanations above:
- The ball striking a wall (option a) will not accelerate.
- The gas balloon (option b), the man in a parachute (option c), and the airplane in horizontal flight (option e) will accelerate.
- The rocket fired straight up (option d) will not accelerate.
Therefore, the correct answer is option a) a ball striking a wall, in which the force of the ball on the wall is equal to the force of the wall on the ball.