A-Level Physics H1 Quiz - Mechanics (Answer Key)
1.
(a) p=mv [1]
(b) K=21mv2 [1]
2.
p=mv⟹v=p/m
K=21mv2=21m(p/m)2=p2/2m
m=p2/2K=(12.0)2/(2×36.0)=144/72=2.0 kg
[M1 for formula/substitution, M1 for rearrangement, A1 for 2.0 kg]
3.
s=ut+21at2⟹20=0+21(9.81)t2
t2=40/9.81≈4.077
t=2.02 s
[M1 for equation, A1 for 2.02 s]
4.
Graph should show v starting at 0, increasing with a decreasing gradient (concave down), and leveling off to a horizontal line (terminal velocity). [2]
5.
As speed increases, the upward air resistance (drag) increases. [1]
The net downward force (W−Drag) decreases, resulting in a decrease in acceleration. [1]
6.
0 m s−2 (No horizontal forces act on the projectile). [1]
7.
In a closed/isolated system [1], the total linear momentum remains constant provided no external forces act. [1]
8.
Total momentum before = Total momentum after
(1.5×2.0)+(2.5×−1.0)=(1.5+2.5)v
3.0−2.5=4.0v
0.5=4.0v⟹v=0.125 m s−1 (in direction of A)
[M1 for momentum conservation, M1 for substitution, A1 for 0.125 m/s]
9.
Kinitial=21(1.5)(2)2+21(2.5)(1)2=3.0+1.25=4.25 J
Kfinal=21(4.0)(0.125)2=0.03125 J
ΔK=4.25−0.03125=4.21875 J (Loss of energy)
Conclusion: Inelastic collision.
[M1 for initial KE, M1 for final KE, M1 for comparison, A1 for "Inelastic"]
10.
Impulse=Δp=m(v−u)
Taking direction of impact as positive: u=15,v=−10
Impulse=0.2(−10−15)=0.2(−25)=−5.0 N s
Magnitude = 5.0 N s
[M1 for Δp formula, M1 for correct sign/substitution, A1 for 5.0 N s]
11.
F=ma
F=m(dv/dt)
Ft=m(v−u)=Δp
[M1 for F=ma, A1 for linking to Δp]
12.
m1u1+m2u2=(m1+m2)v
(0.050×u)+(2.0×0)=(2.05)×1.5
0.050u=3.075
u=61.5 m s−1
[M1 for conservation of momentum, M1 for substitution, A1 for 61.5 m/s]
13.
The collision is inelastic. [1]
Energy is dissipated as heat/sound or used in the deformation of the wooden block. [1]
14.
Diagram must show:
- Weight of plank (200 N) acting at 2.0 m (center). [1]
- Weight of person (600 N) acting at 1.0 m from A. [1]
- Upward reaction forces RA and RB at the ends. [1]
15.
Take moments about pivot B:
∑Clockwise=∑Anti-clockwise
RA(4.0)=(600×3.0)+(200×2.0)
4RA=1800+400=2200
RA=550 N
[M1 for moment equation, M1 for substitution, A1 for 550 N]
16.
Constant velocity ⟹ Net force = 0.
F=mgsin(30∘)
F=5.0×9.81×0.5=24.525 N
[M1 for mgsinθ, M1 for substitution, A1 for 24.5 N]
17.
W=mgh=2.0×9.81×1.5=29.43 J
P=W/t=29.43/0.8=36.7875 W
[M1 for work done, M1 for power formula, A1 for 36.8 W]
18.
Ep=21kx2=21(500)(0.04)2
Ep=250×0.0016=0.4 J
[M1 for formula, A1 for 0.4 J]
19.
W=ΔKE=21mv2−0
W=21(1200)(25)2=600×625=375,000 J
[M1 for 21mv2, M1 for substitution, A1 for 3.75×105 J]
20.
- The vector sum of all forces must be zero (∑F=0). [1]
- The sum of moments about any point must be zero (∑τ=0). [1]