# Worksheet: Work

In this worksheet, we will practice calculating the work done by a force as the product of the force's magnitude and the distance through which the force acts.

**Q4: **

A bullet shot from a rifle has mass of 9.3 g. The bullet travels horizontally at 330 m/s. The bullet strikes a large bag of sand, penetrating the bag to a horizontal distance of 26 cm before coming to rest. Find the magnitude of the average retarding force that acts on the bullet. Ignore any vertical motion of the bullet.

**Q8: **

You are participating in the Iditarod, and your sled dogs are pulling you across a frozen lake with a force of 1,200 N while a 300 N wind is blowing at you at 135 degrees from your direction of travel.

What is the total forward force?

Does the wind increase or decrease your kinetic energy?

- ADecrease
- BIncrease

**Q9: **

A 2,000 kg airplane is coming in for landing with a velocity whose direction is 5 degrees below the horizontal and with a drag force of 40 kN acting directly rearward. Kinetic energy will due to the net force of .

- Aincrease, 45 kN
- Bdecrease, 40 kN
- Cdecrease, 45 kN
- Dincrease, 20 kN
- Edecrease, 20 kN

**Q10: **

A crane is lifting construction materials from the ground to an elevation of 60 m. Over the first 10 m, the motor linearly increases the force it exerts from 0 kN to 10 kN. It exerts that constant force for the next 40 m then winds down to 0 N again over the last 10 m, as shown in the figure. What is the total work done on the construction materials?

**Q13: **

A couch is repositioned on a horizontally aligned living room floor. The first repositioning of the couch involves pushing the couch a distance of 3.0 m parallel to one wall of the room, and then a distance of 1.0 m perpendicular to the 3.0 m distance. The second repositioning of the couch returns the couch to its initial position, but this time without any change of direction. The normal reaction force on the couch from the floor is 1.0 kN and the coefficient of kinetic friction between the couch and the floor is 0.60.

How much work is done by friction on the couch during its first repositioning?

How much total work is done against friction by the couch during both of its repositionings?

**Q14: **

An object moves along a parabolic path , corresponding to the equation from the origin m to the point m under the action of a force The same object moves along the path , corresponding to the equation , also from the origin m to the point m.

Calculate the work done by along the path .

Calculate the work done by along the path .