Hewitt 7.4 hw

Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distances compare?

• It takes twice the work and twice the stopping distance.
• There is no change in the work and stopping distance.
• It takes half the work and half the stopping distance.
• It takes four times the work and four times the stopping distance.

If you push a crate horizontally with 100 N across a 10-m factory floor and the friction between the crate and the floor is a steady 70 N, how much kinetic energy does the crate gain?

• 1,000 J
• 300 J
• 700 J
• 400 J