Physics Jamb Questions

1. The inner diameter of a test tube can be measured accurately using a

• A. micrometer screw guage
• B. pair of dividers
• C. metre rule
• D. pair of vernier calipers

Correct Answer: Option D

2. Two bodies have masses in the ratio 3:1. They experience forces which impart to them acceleration in the ratio 2:9 respectively. Find the ratio of forces the masses experienced.

• A. 1 : 4
• B. 2 : 1
• C. 2 : 3
• D. 2 : 5

Correct Answer: Option C

Explanation

Let the forces be F1, and F2.
F1 = m1 a1 = 3 x 2 = 6N

F2 = m2 a2 = 1 x 9 = 9N

F1 : F2 = 6:9 = 2:3

Thus ratio of forces is 2:3

3.  Particles of mass 10^-2kg is fixed to the tip of a fan blade which rotates with angular velocity of 100rad-1. If the radius of the blade is 0.2m, the centripetal force is

• A. 2 N
• B. 20 N
• C. 200 N
• D. 400 N

Correct Answer: Option B

Explanation

F = mv2r

= mω2r
(Since V = ωr)
F = 10−2
x 1002 x 0.2

F =20 N

4.  a lead bullet of mass 0.05kg is fired with a velocity of 200ms^-1 into a lead block of mass 0.95kg. Given that the lead block can move freely, the final kinetic energy after impact is

• A. 50 J
• B. 100 J
• C. 150 J
• D. 200 J

Correct Answer: Option A

Explanation

From principle of conservation of linear momentum,
(0.05 x 200) - (0.95 x 0) = (0.05 + 0.95) x V (since collision is inelastic).

Thus V = 10m/s.

K.E = 1/2 (0.05 + 0.95) x 10²

K.E = 1/2 (1 x 100) = 50 J 

5. A ball of mass 0.1kg is thrown vertically upwards with a speed of 10ms^-1 from the top of a tower 10m high. Neglecting air resistance, its total energy just before hitting the ground is

(take g = 10ms^-2)

• A. 5 J
• B. 10 J
• C. 15 J
• D. 20 J

Correct Answer: Option C

Explanation

Height h = 1/2 (U²/g) = 10²/20 = 5m

Energy before hitting ground is = P.E at the height of 15m.

P.E = mgh = 0.1 x 10 x 15 = 15 J

6.  A car of mass 800kg attains a speed of 25m/s in 20 secs. The power developed in the engine is

• A. 1 . 25 x 10⁴ W
• B. 2 . 50 x 10⁴ W
• C. 1 . 25 x 10⁶W
• D. 2 . 50 x 10⁶ W

Correct Answer: Option B

Explanation

Power = Force x distancetime

= m(v−u)t×v

800(25−0)20×25 = 2.5 x 104
watts

7. 

When the brakes in a car are applied, the frictional force force on the tyres is

• A. is a disadvantage because it is in the direction of the motion of the car
• B. is a disadvantage because it is in the opposite direction of the motion of the car
• C. is an advantage because it is in the direction of the motion of the car
• D. is an advantage because it is in the opposite direction of the motion of the car

Correct Answer: Option D

8.  If the stress on a wire is 10⁷NM^-2 and the wire is stretched from its original length of 10.00 cm to 10.05 cm. The young's modulus of the wire is

• A. 5 . 0 x 10⁴ Nm^-2
• B. 5 . 0 x 10⁵ Nm^-2
• C. 2 . 0 x 10⁸ Nm^-2
• D. 2 . 0 x 10⁹ Nm^-2

Correct Answer: Option D

Explanation

Y = stress/strain, but stress = 10⁷Nm^-2 (given).

Strain = e/l₀. = (10.05 - 10.00)/10.00 = 0.005

Thus Y = 10⁷/0.005 = 2 . 0 x 10⁹Nm^-2

⁹  When temperature of a liquid increases, its surface tension

• A. Decreases
• B. Increases
• C. Remain Constant
• D. Increases then decreases

Correct Answer: Option A 

10 .A solid weigh 10 .00 N in air, 6 N when fully immersed in water and 7 . 0 N when fully immersed in a liquid X. Calculate the relative density of the liquid, X.

• A. 5/3
• B. 4/3
• C. 3/4
• D. 7/10

Correct Answer: Option C

Explanation

R.D = loss in weight in liquid X loss in weight in water.

R.D = (10 - 7)/(10 - 6) = 3/4