Exam 2—PHYS 201
Chapters 4-7
3 October 2007
Name_________________________
r
1)(15 pts) The velocity v of a particle moving in the xy plane is given by
r
r
v = (3.0t − 2.0t 2 )iˆ + 7.0 ˆj , with v in meters per second and t (>0) in seconds.
a) What is the acceleration when t=2.0 seconds?
b) When (if ever) is the acceleration zero?
c) When (if ever) is the velocity zero?
d) What (if ever) does the speed equal 10 m/s?
2) (25 pts) In this figure, a ball is thrown up onto a roof, landing 5.00 s later at a height of
h=25.0 m above the release level. The balls path just before landing is angled at θ=55○
with the roof.
a) (pts) Find the horizontal distance d the ball travels.
b) ( pts) What is the magnitude of the ball’s initial velocity?
c) ( pts) What is the angle (relative to the horizontal) of the ball’s initial
velocity?
3) (30 pts) Two blocks, of weights 3.7 and 8.0 N (blocks A and B, respectively), are
connected by a massless string on a 20○ inclined plane, with the lighter block leading .
The coefficient of kinetic friction between block A and the plane is 0.10; the coefficient
of kinetic friction between block B and the plane is 0.20. Find the magnitude of the
acceleration of the blocks and the tension in the string.
a) Acceleration.
b) Tension.
4) (20 pts) In this figure, a car is driven at constant speed of 20 m/s over a circular hill
and then into a circular valley with the same radius. At the top of the hill, the normal
force on the driver from the car seat is 10 N. The driver’s mass is 100 kg. If the speed of
the car is 20 m/s, what is the magnitude of the normal force on the driver from the seat
when the car passes through the bottom of the valley?
r
5) (10 pts) A floating ice block is pushed through a displacement d = (10m)iˆ − (25m) ˆj
along a straight embankment by rushing water, which exerts a force
r
F = (100 N )iˆ − (340 N ) ˆj on the block. How much work does the force do on the block
during the displacement?