A pebble of mass 0.05 kg is thrown vertically upwards. Give the direction and magnitude of the net force on the pebble,
(a) during its upward motion, .
(b) during its downward motion,
(c) at the highest point where it is momentarily at rest. Do your answers change if the pebble was thrown at an angle of 45° with the horizontal direction 1 Ignore air resistance.
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(Class-11th)
Answers
Answer:
0.5ɴ, ɪɴ ᴠᴇʀᴛɪᴄᴀʟʟʏ ᴅᴏᴡɴᴡᴀʀᴅ ᴅɪʀᴇᴄᴛɪᴏɴ, ɪɴ ᴀʟʟ ᴄᴀꜱᴇꜱ
ᴀᴄᴄᴇʟᴇʀᴀᴛɪᴏɴ ᴅᴜᴇ ᴛᴏ ɢʀᴀᴠɪᴛʏ, ɪʀʀᴇꜱᴘᴇᴄᴛɪᴠᴇ ᴏꜰ ᴛʜᴇ ᴅɪʀᴇᴄᴛɪᴏɴ ᴏꜰ ᴍᴏᴛɪᴏɴ ᴏꜰ ᴀɴ ᴏʙᴊᴇᴄᴛ, ᴀʟᴡᴀʏꜱ ᴀᴄᴛꜱ ᴅᴏᴡɴᴡᴀʀᴅ. ᴛʜᴇ ɢʀᴀᴠɪᴛᴀᴛɪᴏɴᴀʟ ꜰᴏʀᴄᴇ ɪꜱ ᴛʜᴇ ᴏɴʟʏ ꜰᴏʀᴄᴇ ᴛʜᴀᴛ ᴀᴄᴛꜱ ᴏɴ ᴛʜᴇ ᴘᴇʙʙʟᴇ ɪɴ ᴀʟʟ ᴛʜʀᴇᴇ ᴄᴀꜱᴇꜱ. ɪᴛꜱ ᴍᴀɢɴɪᴛᴜᴅᴇ ɪꜱ ɢɪᴠᴇɴ ʙʏ ɴᴇᴡᴛᴏɴꜱ ꜱᴇᴄᴏɴᴅ ʟᴀᴡ ᴏꜰ ᴍᴏᴛɪᴏɴ ᴀꜱ:
ꜰ=ᴍᴀ
ᴡʜᴇʀᴇ,
ꜰ=ɴᴇᴛ ꜰᴏʀᴄᴇ
ᴍ= ᴍᴀꜱꜱ ᴏꜰ ᴛʜᴇ ᴘᴇʙʙʟᴇ=0.05ᴋɢ
ᴀ=ɢ=10ᴍ/ꜱ²
ꜰ=0.05 × 10=0.5ɴ
ᴛʜᴇ ɴᴇᴛ ꜰᴏʀᴄᴇ ᴏɴ ᴛʜᴇ ᴘᴇʙʙʟᴇ ɪɴ ᴀʟʟ ᴛʜʀᴇᴇ ᴄᴀꜱᴇꜱ ɪꜱ 0.5ɴ ᴀɴᴅ ᴛʜɪꜱ ꜰᴏʀᴄᴇ ᴀᴄᴛꜱ ɪɴ ᴛʜᴇ ᴅᴏᴡɴᴡᴀʀᴅ ᴅɪʀᴇᴄᴛɪᴏɴ.
ɪꜰ ᴛʜᴇ ᴘᴇʙʙʟᴇ ɪꜱ ᴛʜʀᴏᴡɴ ᴀᴛ ᴀɴ ᴀɴɢʟᴇ ᴏꜰ 45° ᴡɪᴛʜ ᴛʜᴇ ʜᴏʀɪᴢᴏɴᴛᴀʟ ᴅɪʀᴇᴄᴛɪᴏɴ, ɪᴛ ᴡɪʟʟ ʜᴀᴠᴇ ʙᴏᴛʜ ᴛʜᴇ ʜᴏʀɪᴢᴏɴᴛᴀʟ ᴀɴᴅ ᴠᴇʀᴛɪᴄᴀʟ ᴄᴏᴍᴘᴏɴᴇɴᴛꜱ ᴏꜰ ᴠᴇʟᴏᴄɪᴛʏ.
ᴀᴛ ᴛʜᴇ ʜɪɢʜᴇꜱᴛ ᴘᴏɪɴᴛ, ᴏɴʟʏ ᴛʜᴇ ᴠᴇʀᴛɪᴄᴀʟ ᴄᴏᴍᴘᴏɴᴇɴᴛ ᴏꜰ ᴠᴇʟᴏᴄɪᴛʏ ʙᴇᴄᴏᴍᴇꜱ ᴢᴇʀᴏ. ʜᴏᴡᴇᴠᴇʀ, ᴛʜᴇ ᴘᴇʙʙʟᴇ ᴡɪʟʟ ʜᴀᴠᴇ ᴛʜᴇ ʜᴏʀɪᴢᴏɴᴛᴀʟ ᴄᴏᴍᴘᴏɴᴇɴᴛ ᴏꜰ ᴠᴇʟᴏᴄɪᴛʏ ᴛʜʀᴏᴜɢʜᴏᴜᴛ ɪᴛꜱ ᴍᴏᴛɪᴏɴ. ᴛʜɪꜱ ᴄᴏᴍᴘᴏɴᴇɴᴛ ᴏꜰ ᴠᴇʟᴏᴄɪᴛʏ ᴘʀᴏᴅᴜᴄᴇꜱ ɴᴏ ᴇꜰꜰᴇᴄᴛ ᴏɴ ᴛʜᴇ ɴᴇᴛ ꜰᴏʀᴄᴇ ᴀᴄᴛɪɴɢ ᴏɴ ᴛʜᴇ ᴘᴇʙʙʟᴇ.
Answer:
0.5N, in vertically downward direction, in all cases
Acceleration due to gravity, irrespective of the direction of motion of an object, always acts downward. The gravitational force is the only force that acts on the pebble in all three cases. Its magnitude is given by Newtons second law of motion as:
F=ma
Where,
F=Net force
m= Mass of the pebble=0.05kg
a=g=10m/s2
F=0.05 × 10=0.5N
The net force on the pebble in all three cases is 0.5N and this force acts in the downward direction.
If the pebble is thrown at an angle of 45o with the horizontal direction, it will have both the horizontal and vertical components of velocity. At the highest point, only the vertical component of velocity becomes zero. However, the pebble will have the horizontal component of velocity throughout its motion. This component of velocity produces no effect on the net force acting on the pebble.