PHY 121
Ch 7 to 10 Exam
Olaf (of 70 kg) is standing on a sheet of frictionless
ice that covers the football stadium parking lot in
Buffalo, New York. A friend throws Olaf a massive
ball of mass 5.00 kg that is traveling horizontally at
10.0 m/s. (a) If the ball hits Olaf and bounces off
his chest horizontally at 8.00 m/s in the opposite
direction, what is his speed after the collision? (b)
If the ball is in contact with Olaf for 0.05 seconds,
what force was imparted to Olaf?
Name
M volaf + m vball = M volaf_final + m vball_final
1/1
5/5
1/1
7/7
1/1 1/1 7/7 1/1
F (.05) = 5 (10 - -8 )
F = 1800 N
14/14
1/1 6/6
2
12/12
k (x ) = m ω (L+x)
1500(x) = 5(52)(.2+x)
x = 0.0182 meters
R = .2182 meters
A 20 kg block is connected to a 30 kg block by a string that passes over a
frictionless pulley. The 30 kg block is connected to a spring that has negligible
mass and a force constant of 400 N/m. The spring is unstretched as shown.
The 20 kg block is pulled 8 cm down the incline and is then released from rest.
The frictional coefficient between the 20 kg block on the ramp is 0.1. The ramp
makes a 30 degree angle above the floor. Find the speed the blocks when they
pass through their original positions.
Einit
=
Efinal
Uspring + U20 + U30 + KE – Ffd = Uspring + U20 + U30 + KE
8/8
5/5
8/ 8
½ k x2 + 0 + 30g(h) +
– Ffd =
2
½400(.08)
+ 300(.08) – Ffd =
25.28 – µ cos30mg d =
v = 0.797 m/s
5/5
1/1
7/7
70 (0) + 5 (10) = 70 (volaf_final) + 5 (-8)
volaf-final = 9/7 m/s
(b)
F (Δt ) = Δ m v
Fc = m v 2 / r
Fc = m (ω r)2 / r
k (x ) = m ω2 r
An object of mass M = 5.00 kg is attached to a
spring with spring constant k = 1500 N/m whose
unstretched length is L = 0.200 m, and whose far
end is fixed to a shaft that is rotating on a
frictionless tabletop with an angular speed of 5.00
radian/sec. Find the radius at which the mass
rotates without moving toward or away from the
origin.
1/1
8/ 8
0 + 20(g)sin30(h) + 0 + ½ mv2
0 + 200 (½) (.08) + ½(20+30)v2
0 +
8
+
25v2