# Warm-Up Exercise for lecture 5

## Due 8:00 am, Tues, 15 Sep 2009

Physics 105, Fall 2009

Newton's first law states that, in the absence of any forces, an object in motion will
☑ remain in motion forever
☐ eventually come to rest.

The engine on a fighter airplane can exert a force of 105,840 N (24,000 pounds). The take-off mass of the plane is 16,875 kg. (It weighs 37,500 pounds.) If you mounted this aircraft engine on your car, what acceleration would you get? (Please use metric units. The data in pounds are given for comparison. Use a reasonable estimate for the mass of your car. A kilogram mass weighs 2.2 pounds.)
☐ less than 10 m/s
☑ between 10 and 100 m/s
☐ between 100 and 200 m/s
☐ more than 200 m/s

If I push on an object which is at rest (like the wall), then the force exerted by my hand on the object will be equal to the force exerted by the object on my hand. However, if I push on an object, causing it to accelerate, then the force exerted by my hand on the object will be
☐ greater than
☐ less than
☑ still equal to
the force exerted by the object on my hand.

Ralph asked me a question the other day. Suppose he's driving his car and a bug hits his windshield. The bug is totally smashed, but the windshield is unaffected. Doesn't this mean that the force exerted by the windshield on the bug is greater than the force exerted by the bug on the windshield? How would you answer his question?
The force is still the same. But because the masses of the objects are so extremely different, the same amount of force will produce very different accelerations. Also, the windshield of the car is much stronger than the bug.