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20° 3. A 7 kg crate is being pulled by a force that is applied at 20° with the horizontal as shown in the diagram. If the force of friction between the crate and the floor is 15 N and the crate moves with a constant velocity, what is the pulling force, F? [A: F = 16 N] 7 kg a 4. The diagram below shows a worker using a rope to pull a cart. The worker's pull on the handle of the cart is at an angle of 50°. The cart is loaded with soil and has a mass of 155 kg. If he pulls the cart against a resistive (drag) force of 50 N, what force does the worker apply to cause a constant velocity? [A: F = 77.8 N] F 5. A block of mass 18 kg is pushed against a rough fixed wall by a force F of 40 N. Determine: • The frictional force between the block and the surface. [A: F1 = 180 N] The normal force acting on the block from the wall. [A: Fn = 40 N] 6. A uniform building brick is pulled along rough ground by a force scale as shown in the diagram. [The mass of the brick is 2.5 kg] A. When the brick is pulled at constant speed the reading on the force scale is 8.2 N. Determine the force of friction between the brick and the ground. [A: F+ = 7.7 N] B. (i) Calculate the vertical component of the 8.2 N force. [A: Fx = 2.8 N] (ii) Determine the force that the ground [Normal Force] exerts on the brick and state the direction of this force. [A: F = 22.2 N upward (FN)]