A skateboarder of mass 55 kg is riding on a level surface. The skateboard has a push force of 150 N and a coefficient of kinetic friction of 0.2. The skateboarder's legs become tired after 15 s and he coasts to a stop. Determine the distance covered by the skateboarder at the instant they finally stop. Consider the skateboarder starts from rest.

A truck carrying drum-shaped cable reels of electrical wires loses control and bangs on the roadside wall. One of the cable reels rolls down from the truck and stops 30 m from the truck. Find the speed of the cable reel if its mass is 550 kg and the coefficient of kinetic friction is 0.45.

A crate of mass 25 kg is placed on a ramp inclined at an angle of 30° with the horizontal. The crate has a coefficient of static friction with the ramp of 0.4 and a coefficient of kinetic friction of 0.2. The ramp has a length of 10 m. Determine the acceleration of the crate down the ramp and the time required by the crate to come to reach the bottom of the ramp. Consider the direction pointing up the ramp to be positive.

A 350 kg rubber barrel is rolled on level concrete ground at 5 m/s. Determine the distance the barrel will cover before it halts.

A cart moving on a level surface with a speed of 10 m/s is carrying a bag of mass 20 kg. The coefficients of friction between the bag and the cart are μₛ = 0.35 and μₖ = 0.22. The speed of the cart goes on decreasing and ultimately it stops. Determine the minimum distance that the cart can cover before stopping with the bag not moving from its position.

A steel crate with a mass of 200 kg is placed on top of a large aluminum platform with a mass of 500 kg. The platform is moving along a frictionless factory floor. The coefficient of kinetic and static friction between the steel crate and the aluminum platform is the same and denoted by μ. An external force is applied to the aluminum platform to move both the platform and the crate at a constant acceleration of 2.5 m/s².

a) Determine the force that must be applied to the aluminum platform without causing the steel crate to slide on the platform.

b) If the coefficient of friction between the steel crate and the aluminum platform is reduced to half of its original value, determine the force that must be applied to keep the platform accelerating at 2.5 m/s².