Review

Motion and Forces Test

Starter Q 12-5 Forces

• Two different forces interact on a cart, one is 8 N and the other is 6 N. What is the minimum and maximum net force that could be acting on the cart? Draw two free body diagrams respresenting

Forces

• Two different forces interact on a cart, one is 8 N and the other is 6 N. What is the minimum and maximum net force that could be acting on the cart?

• Answer: minimum net force 8 N- 6 N = 2 N maximum net force 8 N + 6 N = 14 N

Forces

• A 4000 N car is driving down the road at a constant velocity of 60 mph north. The force that the engine applies to the wheels is 2500 N. Find the normal force acting on the car and the combined amount of air resistance and friction acting on the car. Draw a free body diagram showing all four forces.

Forces

• A 4000 N car is driving down the road at a constant velocity of 60 mph north. The force that the engine applies to the wheels is 2500 N. Find the normal force acting on the car and the combined amount of air resistance and friction acting on the car. Draw a free body diagram showing all four forces.

• Answer: – F normal = 4000 N – F air and friction = 2500 N

Forces

• The same 4000 N car is driving down the road and accelerates to the north using a force of 3200 N. Find the net force acting on the car and the direction that the net force is acting. Assume the same air resistance and friction as in the previous problem. Draw a free body diagram showing all four forces.

Forces

• The same 4000 N car is driving down the road and accelerates to the north using a force of 3200 N. Find the net force acting on the car and the direction that the net force is acting. Assume the same air resistance and friction as in the previous problem. Draw a free body diagram showing all four forces.

• Answer: – F net = 3200 N – 2500 N = 700 N to the north

Determine the net force acting on the box in each panel.

50 N 50 N 50 N 30 N 50 N

70 N

A B C

A B C

Which panel(s) show unbalanced force? ________________

Which panel(s) show balanced force? ________________

Which panel(s) show net force > zero? ________________Which panel(s) show acceleration? ________________

Identify the two forces acting in this photograph. Then complete the fill-in-the-blank question to the left.

(zero, unbalanced, increasing, balanced, 9.8 m/s2, and constant.)

This man is falling at terminal velocity. At terminal velocity, the forces are _____________, the falling speed is _____________ and the rate of acceleration is ____________.

Identify the two forces acting in this photograph. Then complete the fill-in-the-blank question to the left.

(zero, unbalanced, increasing, balanced, 9.8 m/s2, and constant.)

This man is falling at terminal velocity. At terminal velocity, the forces are __balanced_, the falling speed is ____constant__ and the rate of acceleration is zero.

Air resistance

Force of gravity or weight

Falling Objects

Which object hits the ground first? Last? Which experiences the greatest net force (difference between air resistance and weight or F grav)? Which will experience the greatest rate of acceleration? The least?

Least surface area?Greatest weight?

Greatest surface area?

Falling Objects

Which object hits the ground first? Last? Which experiences the greatest net force (difference between air resistance and weight or F grav)? Which will experience the greatest rate of acceleration? The least?

Least surface area?Greatest weight?

Greatest surface area?

Greatest Net Force?

Greatest Acceleration?

Least Acceleration?

Which two factors influence the force of air resistance acting on a falling object?

Surface area and Speed

Which two factors influence the amount of gravity that exists between two objects?

Mass of the objects and the distance between the objects.

Which two motions act at the same time to cause an object to act as a projectile?

Horizontal motion (constant speed)

vertical motion (acceleration)