The mass of a two-person bobsled (without the people) is 300 kg. The bobsled starts from rest, and then the crew members push the sled with a constant force of 430 N on a flat, horizontal snowy surface for 25 meters before jumping aboard. The frictional force on the bobsled due to snow is 140 N, and air resistance on the bobsled is 20 N. How long of time does it take the crew members to push the bobsled 25 meters?

	a.	about 2.3 seconds
	b.	about 5.1 seconds
	c.	about 7.5 seconds
	d.	about 8.5 seconds
	e.	about 9.8 seconds

The mass of a two-person bobsled (without the people) is 300 kg. The bobsled starts from rest, and then the crew members push the sled with a constant force of 430 N on a flat, horizontal snowy surface for 25 meters before jumping aboard. The frictional force on the bobsled due to snow is 140 N, and air resistance on the bobsled is 20 N. The net external force on the bobsled while the crew members are pushing the bobsled is:

	a.	590 N.
	b.	570 N.
	c.	430 N.
	d.	290 N.
	e.	270 N.

The mass of a two-person bobsled (without the people) is 300 kg. The bobsled starts from rest, and then the crew members push the sled with a constant force of 430 N on a flat, horizontal snowy surface for 25 meters before jumping aboard. The frictional force on the bobsled due to snow is 140 N, and air resistance on the bobsled is 20 N. The acceleration of the bobsled while the crew members are pushing the bobsled is:

	a.	about 0.70 m/s2.
	b.	about 0.90 m/s2.
	c.	about 1.4 m/s2.
	d.	about 1.9 m/s2.
	e.	about 9.8 m/s2.

The mass of a two-person bobsled (without the people) is 300 kg. The bobsled starts from rest, and then the crew members push the sled with a constant force of 430 N on a flat, horizontal snowy surface for 25 meters before jumping aboard. The frictional force on the bobsled due to snow is 140 N, and air resistance on the bobsled is 20 N. What is the instantaneous speed of the bobsled after the crew members push it for 25 meters?

	a.	about 22 m/s.
	b.	about 15 m/s.
	c.	about 8.4 m/s.
	d.	about 6.7 m/s.
	e.	about 5.9 m/s.

A torque of 80 Nm is applied to a wheel about its axle and the wheel rotates in the clockwise direction. A frictional torque of 20 Nm acts at the wheel's axle. What is the net external torque about the axle of the wheel?

	a.	20 Nm
	b.	60 Nm
	c.	80 Nm
	d.	100 Nm
	e.	none of the items

The increasing speed of a spinning figure skater as she pulls her arms closer to her body is:

	a.	an optical illusion caused by making the radius of spin smaller.
	b.	produced by a torque generated by the skater pushing on the ice.
	c.	is a consequence of the fact that her angular momentum is constant.
	d.	a violation of conservation of energy.
	e.	an example of conversion of kinetic energy into potential energy.

If a ruler lying on a level, smooth, horizontal surface is pushed exactly at its midpoint, then:

	a.	the ruler moves forward in the direction of the net applied force, but it does not rotate.
	b.	the ruler rotates clockwise.
	c.	the ruler rotates counterclockwise.
	d.	there is a nonzero torque on the ruler.
	e.	the ruler will have a positive rotational acceleration.