PHY 2053, Spring 2009, Quiz 6 — Whiting
1. A mechanic pushes a 3.00 × 103 kg car from rest to a speed of v, doing 6,000 J of work in
the process. During this time the car moves 25.0 m. Neglecting friction between the car and
the road, find:
a) v, and
1
W = mv 2 ⇒
2
v=
r
2W
=
m
r
2 × 6000
= 2m/s.
3000
b) the horizontal force exerted on the car.
W = F × d × cos(θ) ⇒
F =
W
6000
=
= 240 N, since θ = 0◦ .
d × cos(θ)
25.0
2. An archer pulls her bowstring back 0.350 m by exerting a force that increases uniformly
from zero to 245 N.
a) What is the equivalent spring constant of the bow?
Farcher = k × ∆x ⇒
k=
245
Farcher
=
= 700 N/m.
∆x
0.350
b) How much work does the archer do in pulling the bow?
W =
1
1
Farcher × ∆x = k × (∆x)2 = 0.500 × 245 × 0.350 = 42.875 J.
2
2