A block is at rest on a horizontal frictional surface. A string is attached to the block, and is pulled with a force of 65.4 N at an angle theta above the horizontal. After the block is pulled through a distance of 1.35 m, its speed is 1.69 m/s, and 85.0 J of work has been done on it.  Part A: Find the mass of the block.  Part B: What is the work done by normal force in this case? Explain.  Part C: Let’s say you are lifting this block in air instead of pulling it on the ground and then let go of it. How high will you have to lift this block to reach this same speed of 1.69 m/s moments before it touches the ground?

Consider an object of mass m = 4 kg on a frictionless table. The object experiences a repulsive force F = a/x2 + b/x, where F is in newtons and x is the position of the object relative to the origin. Write an expression for the work done by the repulsive force on the object as it moves from an initial position of x1 to a final position of x2.    If the object starts at a position of x1 = 8.5 m apart, how much work, in joules, is required by an external force to bring it to a position of x2 = 2.5 m apart when a = 19 and b = 11?    If the object starts at rest at a position x3 = 1.3 m and is released, at what speed v, in meters per second, will the object be moving when it is at position x4 = 12.5 m?

A shopper pushes a grocery cart for a distance 21.5 m at constant speed on level ground, against a 32.5 N frictional force. He pushes in a direction 26.5° below the horizontal. What is the work done on the cart by the gravitational force, in joules? What is the work done on the cart by the shopper, in joules?  Find the magnitude of the force, in newtons, that the shopper exerts on the cart. What is the total work done on the cart, in joules?

A-C please!