Force and Newton's Laws

What force needs to be applied in order to accelerate a 9 mg sample of blood at 40 m/s^2? A. 3.6 x 10^2 mN B. 3.6 x 10^-4 N C. 3.6 x 10^-7 uN D. 3.6 x 10-7 uN

B. 3.6 x 10^-4 N (Newton's second law says that acceleration is directly proportional to the net force. This is expressed by F = ma, where "m" represents mass "a" represents acceleration. For our answer F to come out in newtons (kg*m/s2), "m" must be in kilograms and "a" must be in m/s2. F = (9 x 10-3 g)(40 m / s2) = (9 x 10-6 kg)(40 m / s2) = 360 x 10-6 N = 3.6 x 10-4 N )

If power is an amount of force applied over a distance in a certain amount of time, by which of the following terms would you multiply units of force to get units of power? A. kg(m^2/s^3) B. (m^2/s^2) C. (m/s) D. s^-1

C. (m/s) (Force is measured in Newtons (N) and equal to the mass (kg) of an object multiplied by the acceleration (m/s2) of that object. Therefore, 1 N = (kg)(m/s2). Power is measured in (newton)(meter)/(second). Following standard SI notation, the units for power would be: [(kg)(m/s2)(m)]/(s) = kg(m2/s3). The question wants us to identify what units we need to multiply by a newton to get the unit for power. If we were to multiply (m/s) by a newton, we would get kg(m2/s3), which is the unit for power.)

Your dog, still chasing after that bouncing rubber ball on the tile floor, suddenly goes sliding across the tile as she attempts to turn around and run back to you. Which of these forces is opposing the forward movement of your dog? A. Spring force as the ball stretches and compresses B. Force of static friction while your dog is sliding along the floor C. Normal force between the floor and your dog D. Drag from the air as your dog runs

D. Drag from the air as your dog runs (Drag from an object moving through the air is known as air resistance. Air resistance is really just friction between the air molecules and whatever is trying to move past them. Air resistance opposes your dog's forward movement.)

What pieces of information do you NOT need to know in order to solve for the gravitational force felt by the Earth from a butterfly pollinating flowers? Select all that apply. A. Distance between the center of the mass of the butterfly and the Earth B. Mass of the butterfly C. Mass of the Earth D. Universal gravitation constant

A. Distance between the center of the mass of the butterfly and the Earth C. Mass of the Earth D. Universal gravitation constant

Which of the following are NOT an underlying force of tension? Select all that apply. A. Gravitational force B. Electromagnetic force C. Force due to friction D. Centripetal force

A. Gravitational force C. Force due to friction D. Centripetal force

Will the acceleration of a mobile x-ray machine be constant if a constant, nonzero net force is applied to push it between inpatient rooms in the hospital? Why? A. Yes. According to Newton's second law, force = (mass) * (acceleration), so acceleration will be constant when a constant force is applied. B. No. According to Newton's first law, an object in motion will stay in motion at constant velocity in the absence of a net external force. C. Yes. According to Newton's second law, force = (mass) * (acceleration), so velocity will be constant when a constant, nonzero net force is applied. D. No. According to Newton's second law, force = mass * (acceleration), so velocity will be constant when a constant net force is applied.

A. Yes. According to Newton's second law, force = (mass) * (acceleration), so acceleration will be constant when a constant force is applied. (Newton's second law states that acceleration is directly proportional to the net force applied. If a constant net force is applied to the machine, its acceleration will be constant as well.)

Which of the following statements about how the force of friction relates to Newton's laws is/are FALSE? Select all that apply. A. According to Newton's third law, when a surface exerts a frictional force on an object, the object exerts a frictional force back on the surface. B. If you push on an object at rest and begin accelerating it forward, the force of friction on the object will act to increase the net acceleration of the object. C. If you push on an object at rest and begin accelerating it forward, the force of friction on the object will act in the same direction as the net force on the object. D. Newton's first law states that an object in motion will remain in motion at a constant velocity if friction is the only force acting on it.

B. If you push on an object at rest and begin accelerating it forward, the force of friction on the object will act to increase the net acceleration of the object. C. If you push on an object at rest and begin accelerating it forward, the force of friction on the object will act in the same direction as the net force on the object. D. Newton's first law states that an object in motion will remain in motion at a constant velocity if friction is the only force acting on it.

Which of the following will cause the normal force between a cat and the surface it is sitting on to decrease? A. Increasing the mass of the cat B. Increasing the angle of incline for the surface the cat is sitting on to 15 degrees C. Increasing the coefficient of static friction D. Raising the cat from the floor to a position on a table that is 5m higher off the group

B. Increasing the angle of incline for the surface the cat is sitting on to 15 degrees (The normal force is the force exerted between two surfaces in contact, at an angle perpendicular to those surfaces, that prevents them from passing through each other. If the surface the cat is sitting on is horizontal, the normal force must be equal to the force of gravity on the cat, since gravity pulls the cat perpendicularly into the surface. However, if the surface is at an angle, the force of gravity does not point perpendicularly into the surface; you could imagine splitting it into two components, one pointing perpendicularly into the surface and the other pointing parallel to the surface, and only the component pointing into the surface will be opposed by the normal force. At such an angle of incline, the component of gravity pointing into the surface (which will have the same magnitude as the normal force) will be equal to (mass)(acceleration due to gravity)(cosθ). Because cosθ is equal to 1 at no incline and is less than 1 at any nonzero angle of incline up to 90°, the normal force will decrease when the angle of incline is increased. Note that at 90°, the normal force goes to zero; this is the case where the surface is completely vertical, so it doesn't support the cat at all!)

An emergency room physician is designing a new textile to be used for special pants and jackets in order to protect motorcycle riders involved in crashes from severe road rash. Which of these values for the coefficient of kinetic friction would be the worst choice if you wanted to minimize the adverse effects of kinetic friction? A. 0.05 B. 0.4 C. 0.8 D. 1.2

D. 1.2 (The force of kinetic friction is directly proportional to the coefficient of kinetic friction. Kinetic friction is the force opposing the motion of the rider as they slide across the highway in the event of a bad crash. The force of kinetic friction is responsible for tearing up the rider's clothes and ultimately their skin, which is known as road rash. In order to minimize these negative effects of kinetic friction, we want the smallest possible coefficient of kinetic friction between the material and the highway. This means we want to stay away from material that has a very high coefficient of kinetic friction with the highway. This is the largest value of the choices listed, so this answer choice gives the coefficient of kinetic friction we most want to avoid.)

An object is pushed forward by a constant force which accelerates it at 17 m/s2. Which of the following interventions will keep the object's acceleration at 17 m/s2? Select all that apply. A. Increasing the force applied by a factor of 1.5 and increasing the mass of the object by a factor of 0.43. B. Increasing the force applied and decreasing the mass of the object. C. Causing the object to maintain a constant velocity D. Increasing the force applied by a factor of 2 and increasing the mass of the object by a factor of 2

D. Increasing the force applied by a factor of 2 and increasing the mass of the object by a factor of 2 (According to Newton's second law, F = ma, an object's acceleration is directly proportional to the net force acting on it but inversely proportional to its mass (this is perhaps more intuitive if rearranged as a = F/m). If the force is doubled but the mass is also doubled, the acceleration will remain unchanged.)