Kinetic Friction Practice Problems

A 35.0 N block is resting on a horizontal floor. The coefficients of static and kinetic friction between the block and the floor are 0.38 and 0.26 respectively. A child is pushing against the block with a horizontal force. Determine the magnitude of the friction force on the crate and its acceleration when the child applies a horizontal steady force of 15.0 N.

A 42.0 N block is resting on a horizontal floor. The coefficients of static and kinetic friction between the block and the floor are 0.46 and 0.29 respectively. A child is leaning against the block applying a horizontal force. Determine the least horizontal force the child must apply to move the crate at constant velocity.

A 29 kg luggage is resting on the floor in your house. You pull the luggage with an increasing horizontal force. The box moves when your pull is greater than 211 N. The luggage moves with a constant velocity of 1.8 m/s when you reduce the pull to 147 N. How hard must you pull to accelerate the box at 1.5 m/s²?

A 25 kg block is resting on a level truck. You pull the box with an increasing horizontal force. The box moves when the pull is greater than 186 N. You realize that the box moves with a constant velocity of 1.4 m/s when you decrease the pull to 114 N. Determine the static and kinetic friction coefficients between the box and the truck.

Kinetic and static friction are determined experimentally by applying a horizontal force on an object until it moves and for some time after it starts moving. In one such experiment, a 86 N box is placed on a rough horizontal bench and pushed by a horizontal force. The graph below shows the friction force on the box as a function of the push. In what regions of the graph does static and kinetic friction occur?

The drag constant, D for an object falling through air depends on the position. The position basically determines the effective cross-sectional area. Determine the terminal speed of a 62 kg skydiver falling through the air in a feet-first position. The drag constant for this position is 0.15 kg/m. Hint: v_t = √(mg/D)

A spherical stone is launched vertically upward. It is experimentally proven that the drag force is proportional to v2 for large objects like baseballs, cars, and bicyclists that don't move too slowly. Determine the vertical component of the stone's acceleration at a moment in time when its speed is half the terminal speed and it is moving downward. Express your answer in terms of g.

In a game, a tennis ball is tossed vertically up in the air. It experiences a drag force proportional to v². Determine the y-component of the ball's acceleration at a period in time when its speed is half the terminal speed and it is moving upward. Express your answer in terms of g.